Select the most appropriate option to fill in the blank 3.
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. collecting.
- In the context of the sentence, "collecting" is the most suitable term.
- It implies that Darwin spent twenty years gathering or accumulating information for his book.
- The other options ("making," "observing," "dispersing") do not fit the context as well.