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。
