Their actions（）the stability and security of the region.

Their actions（）the stability and security of the region.
A、harden
B、frighten
C、brighten
D、threaten
【正确答案】：D
【题目解析】：本题考查动词辨析。harden v. 变硬，变严厉。frighten v. 使惊恐。brighten v. 使更明亮。threaten v. 威胁。句子的主语是“Their actions”，宾语是“the stability and security”，所以只有D选项“威胁”最符合题意。句意：他们的行为对这一地区的稳定和安全造成了威胁。