Thes chemical ,_______to kill biological organisms ,are unsafe and oten not specific in their targets .
A.having designed
B.to design
C.designing
D.designed
网友回答
D解析这题考查过去分词的用法，be designed to do，“被设计做…”，design和chemical是被动的关系，句意是：被设计来杀死生物有机体的化学物质是不安全的，不能完全针对它们的目标。选D。