Answer:
A sudden hush fell on the crowd as Mr. Summers cleared his throat and looked at the list.
Explanation:
The phrase from the excerpt that best reveals how the social environment shifts as the lottery begins is "A sudden hush fell on the crowd as Mr. Summers cleared his throat and looked at the list.".
This is because, by mentioning that there was a sudden silence in the crowd as the lottery numbers were about to be called shows that the social environment shifted as the announcement was about to be made.
