童鞋,in case of和for fear of都是介词短语啊,所以后面都跟名词、代词或doing；
in case(that)和for fear that都是连词词组,后面要跟从句的,in case that意思是“以防万一”引导的是条件状语从句,for fear that（唯恐）引导的是目的状语从句.例子：
他带了一把雨伞以防下雨.He carried an umbrella in case of rain或者in case (that) it rained.
他们悄声说话,唯恐吵醒婴儿.They talked in whisper for fear of waking up the baby或者for fear that they woke up the baby.