【C9】A．WhatB．CauseC．ReasonD．Because

【C18】A．answerB．expressionC．reasonD．effect

A．measureB．luckC．reasonD．sense

【C20】A．keyB．creditC．reasonD．way

A．problemB．causeC．resultD．resource

【C6】A．prospectB．wayC．reasonD．necessity

【C8】A．questionB．argumentC．reasonD．excuse