单选题The video security systems ______.A play an important role in arresting terrorists before they take actionB have cost the U.S. Department of Homeland Security more than $ 40 million so farC are mainly deployed near WashingtonD work better than they hav
题目
单选题
The video security systems ______.
A
play an important role in arresting terrorists before they take action
B
have cost the U.S. Department of Homeland Security more than $ 40 million so far
C
are mainly deployed near Washington
D
work better than they have been expected to