In the following passage type question, some words are missing. Read the sentence carefully and choose the correct option for the third blank. We are living in a time of great and continuing changes. The most obvious _____ of the modern world is the rapid development of science and technology. This has given man a deeper _____ of nature.

Introduction / Context:
This question continues the same descriptive passage about the modern world. Now we focus on the phrase "The most obvious _____ of the modern world". The missing word should describe a characteristic or distinguishing quality of modern times. It must form a natural and meaningful collocation with "the most obvious" and "of the modern world".

Given Data / Assumptions:

• Sentence fragment: "The most obvious _____ of the modern world is the rapid development of science and technology."
• The sentence explains what clearly stands out when we look at today's world.
• The complement of the linking verb "is" is "the rapid development of science and technology".
• Options: part, side, feature, nature.
• We need a noun that can logically connect "modern world" and "development of science and technology".

Concept / Approach:
In descriptive writing, it is common to say "an important feature of the modern world is ..." or "one striking feature of the modern world is ...". The word "feature" means a characteristic, quality, or aspect that stands out. While "part" and "side" are also nouns, they are not as precise here. "Nature" usually refers to inner character or to the physical natural world and does not fit immediately before "of the modern world". Therefore, "feature" is the most suitable and idiomatic choice.

Step-by-Step Solution:

Verification / Alternative check:
Reading the full sentence with "feature", we get "The most obvious feature of the modern world is the rapid development of science and technology." This expresses clearly that among many characteristics, rapid scientific and technological growth is the most striking. The sentence is stylistically typical of essays discussing modernisation and progress, confirming that "feature" is the correct choice.

Why Other Options Are Wrong:
Option A, "part", does not highlight the idea of a characteristic. It would more likely be used if we were dividing the world into segments. Option B, "side", suggests an aspect in the sense of a viewpoint or side of an argument, which does not match the descriptive tone here. Option D, "nature", would require a different construction like "The nature of the modern world is ..." and does not fit well after "The most obvious". Therefore, "feature" is the only choice that gives a clear and natural meaning.

Common Pitfalls:
Students sometimes choose words based only on loose associations, for example linking "nature" with "world". However, cloze questions require sensitivity to fixed or common phrases such as "feature of the modern world". Building familiarity with such phrases through reading helps greatly in choosing the correct option quickly under exam pressure.

Final Answer:
The most suitable word for the third blank is feature, giving the sentence "The most obvious feature of the modern world is the rapid development of science and technology."