In the following passage, some words have been left out. Read the passage carefully and select the correct answer for the blank. With rapid progress in technology in other renewable energy sources, the collapse of oil prices and the expansion in gas projects as a viable and clean alternative, that promise _____.

Introduction / Context:
This final blank in the passage summarises the effect of changes in energy technology and markets on the earlier promise of nuclear power. The sentence lists several present or recent developments and then comments on how they have affected that promise. You need to choose the correct verb phrase that matches the tense and grammar of the sentence and expresses a completed but still relevant change.

Given Data / Assumptions:

• Clause before the blank: With rapid progress in technology in other renewable energy sources, the collapse of oil prices and the expansion in gas projects as a viable and clean alternative.
• Subject of the verb: that promise, referring to the earlier promise of nuclear power.
• Options: to dim, dimming, was dim, has dimmed.
• The context: describing how this promise is no longer as bright as it once was.

Concept / Approach:
The structure with several present or near present developments, then that promise followed by a present perfect verb, is a typical way to say that something has changed over time and the result is still true now. The present perfect form has dimmed shows that the promise has become less bright or less attractive as these developments have occurred. The other forms either do not fit grammatically after that promise or they use a tense that does not match the surrounding context. Choosing the correct auxiliary and past participle combination is the key here.

Step-by-Step Solution:
Step 1: Identify the subject that promise and note that it is singular.Step 2: Recognise that the sentence describes a change that has happened because of the developments mentioned earlier.Step 3: Decide on the tense. Since the factors listed are recent and their effect continues now, present perfect is appropriate.Step 4: Form the present perfect for a singular subject: has plus past participle.Step 5: Use the verb dim in past participle form dimmed, giving has dimmed.Step 6: Insert has dimmed into the sentence and confirm that it reads naturally: that promise has dimmed.

Verification / Alternative check:
Read the whole sentence: With rapid progress in technology in other renewable energy sources, the collapse of oil prices and the expansion in gas projects as a viable and clean alternative, that promise has dimmed. This clearly means that the earlier attractive promise of nuclear power is not as strong now. If we switched to simple past was dim, the sentence would sound as if the promise was always weak, which contradicts the earlier statement that the promise had so far outweighed concerns. Present perfect links the past promise and the present reality appropriately.

Why Other Options Are Wrong:
To dim: This is an infinitive form and cannot function as the main verb of the clause after that promise. It would require a different structure such as began to dim, which is not provided. Dimming: This -ing form could be used in a different construction like that promise is dimming, but by itself it does not fit after the subject without an auxiliary. Was dim: This simple past form suggests a state in the past, not a change caused by recent developments. It also conflicts with the earlier description of the promise as strong. Has dimmed is the only option that captures the idea of a promise that has become weaker over time due to new circumstances.

Common Pitfalls:
Many candidates see an -ing form or infinitive and think it must fit somewhere, but forget that a full clause with a subject usually needs a finite verb that agrees in number and tense. Another common error is to choose simple past whenever the developments mentioned are in the past, without considering whether the result still matters in the present. The present perfect is especially common in analytical writing about trends, and recognising that pattern can help you select the right verb form. Always check agreement (has with a singular subject) and ensure you are not leaving the clause without a proper finite verb.

Final Answer:
The correct verb phrase to complete the sentence is has dimmed, giving the clause that promise has dimmed.