TOEFL Grammar- Choose the right word

ScottsEnglish

Choose the correct word for the following sentence:

The North American wolf was almost extinct in its natural habitat, so its numbers _______________________ by the government until they were stable again.

A. are controlled 
B. were maintain 
C. were regulated 
D. have been counted 

The North American wolf was almost extinct in its natural habitat, so its numbers were regulated by the government until they were stable again.