【单选题】

Questions 11 to 13 are based on the following passage.At the end of the passage, you will be given 15 seconds to answer the questions.

Now listen to the passage.
What was the main harmful effect of the pest killerDDT on bald eaglesA．It limited their supply of fooD、
B．It made their egg shells too fragile.
C．It destroyed many of their nests.
D．It killed many baby bald eagles.