In the following passage, one sentence is missing and has been replaced by a blank. Choose the option that best completes the passage. The passage discusses the morality and legality of nuclear weapons and the responsibility of scientists who work on them.

Introduction / Context:
This question is about paragraph coherence and logical flow. The passage deals with the moral and legal objections to nuclear weapons, and then moves towards the responsibility of scientists who help create them. One sentence has been removed and replaced with a blank. You must choose the sentence that fits logically and smoothly into the argument, strengthening the author's case about the misuse of scientific expertise.

Given Data / Assumptions:

• The passage states that using and producing nuclear weapons is contrary to morality and law.
• It argues that adding legal objections to moral ones reinforces the case against nuclear weapons.
• It then says that the time is ripe to evaluate the responsibility of scientists who knowingly use their expertise to construct such weapons.
• It finishes by questioning whether such valuable skill should be devoted to manufacturing weapons of death in a world of poverty.
• The missing sentence must connect the discussion of moral and legal objections with the focus on scientists and their role.

Concept / Approach:
The best missing sentence should introduce a factual or quantitative element that emphasises how much scientific talent is being absorbed by the armaments industry. This data based assertion provides a strong reason to examine scientists' responsibility and the ethical use of resources. Option A offers exactly such a factual statement about the proportion of skilled scientific manpower engaged in armaments. The other options are more emotional or repetitive and do not serve as an effective bridge between the legal–moral discussion and the call to evaluate responsibility.

Step-by-Step Solution:
Step 1: Read the sentences before the blank. They explain that nuclear weapons are contrary to morality and law, and that combining legal and moral objections reinforces the argument against them.Step 2: Read the sentences after the blank. They say that now is the right time to evaluate the responsibility of scientists who use their expertise to build such weapons and then question whether this skill should be used to create weapons in a poor world.Step 3: Identify what kind of idea would link these two parts. A natural link is a statement showing that a huge amount of scientific talent is involved in arms production, making the moral and legal issue more urgent.Step 4: Examine option A: "Almost 50% of the skilled scientific manpower in the world is now engaged in the armaments industry." This gives a striking statistic and naturally leads to the next sentence about evaluating the responsibility of scientists.Step 5: Check the remaining options and see that they either repeat the idea of conscience (option C), express vague hurt (option B), or attack selfish people in general terms (option D), without adding the same concrete, bridging force as option A.

Verification / Alternative check:
Insert option A explicitly into the passage and read it through. The sequence becomes: moral and legal objections to nuclear weapons, a statistic about half of the world's scientific manpower working in armaments, followed by a call to evaluate scientists' responsibility. This reads smoothly and increases the weight of the argument. Inserting option C would make the passage repeat the idea of conscience just before another sentence about conscience, creating redundancy instead of development.

Why Other Options Are Wrong:
Option B is emotionally worded but does not provide a strong logical bridge or new information. Option C preaches what scientists should do, but the next sentence already discusses evaluating their responsibility, so it becomes repetitive rather than additive. Option D shifts focus to "selfish and careless people" who want to threaten humankind, which diverts attention from scientists themselves and does not connect as tightly with the legal–moral discussion.

Common Pitfalls:
Students sometimes pick the sentence that sounds most emotionally charged or morally strong. However, coherence questions are about which sentence moves the argument forward in a structured way. A good strategy is to look for the sentence that introduces a new, relevant dimension (here, a numerical estimate of manpower) and naturally leads into both what was said before and what comes after.

Final Answer:
The sentence that best completes and strengthens the passage is "Almost 50% of the skilled scientific manpower in the world is now engaged in the armaments industry.", so option A is correct.