The speaker is talking about the water. During winter, the water enters the cracks and freezes and expands. It breaks the stone and makes cracks and when the water melts the holes are bigger. What he is describing is mechanical weathering which is common in nature.
It means extreme danger so the answer is B
The answer is:
A. understand that managing the moon landing while the lunar module had 30 seconds left of fuel required intense concentration.
In the excerpts the narrator mentions the lunar module had 30 seconds left of fuel, so the people who were in charge of the moon landing could not make a mistake, a miscalculation or lose their extraordinary focus. For example, one of the narrators states the men "could not afford to be wrong." Otherwise, the mission could have failed.
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