He gradually ______ that her parents had been right and his decision had to be modified.
 
【正确答案】 A
【答案解析】 句意:他逐渐觉察到她的父母是对的,他必须改变自己的决定。perceive意为“觉察,感知”,符合句意。pioneer开拓,开辟。plague折磨,使苦恼。transform转变,改变。