Answer:
Geologists search rivers, mountains, and caves for clues about how and when the Earth was formed.
Explanation:
This would be an important idea to include in your summary because it contributes to the central idea of the entire passage. The passage is about the work of geologists, and this sentence/idea is the main idea.
Answer:
C. On the way to the city of Riga
Answer:
A) the main idea is what the paragraph is about
Explanation:
from the words main idea you can guess it can't be b or c because that doesn't make sense. its not d as well that's a different topic. so your answer is a which explains it the best. hope it helps you