请教新prep-1-178

Last week local shrimpers held a news conference to take some credit for the resurgence of the rare Kemp's ridley turtle, saying that their compliance with laws requiring that turtle-excluder devices be on shrimp nets protect adult sea turtles.

A. requiring that turtle-excluder devices be on shrimp nets protect

B. requiring turtle-excluder devices on shrimp nets is protecting

C. that require turtle-excluder devices on shrimp nets protect

D. to require turtle-excluder devices on shrimp nets are protecting

E. to require turtle-excluder devices on shrimp nets is protecting

答案是B  想请问is 的主语是谁呢？为什么用单数呢？谢谢~

主语是 their compliance

saying that their compliance with laws requiring turtle-excluder devices on shrimp nets is protecting adult sea turtles.

谢谢nn们~^_^