The underlined 'this' in line 3, paragraph 9 refers to ______.
A.some foreign Power.
B.the security system of some nuclear plants.
C.sabotage by some foreign Power.
D.the attack by some terrorists.

A.A.some
B.
B.the
C.
C.sabotage
D.
D.the

【参考答案】

C
解析：理解题。根据推理，“this”指代的是前一句话中“prevent”的宾语。