Mary is always pleased at the party.
A. to invite; to sing
B. to invite; singing
C. to be invited: to sing
D. to be invited; singing
网友回答
A. to invite; to sing
B. to invite; singing
(答案→)C. to be invited: to sing
D. to be invited; singing
解析：考查非谓语动词。句意：玛丽总是很高兴被邀请在聚会上唱歌。不定式表示具体的将要进行的动作，结合语境可知玛丽是被要邀请的对象，故用被动语态。下文为玛丽的逻辑动作，故用主动语态，选C。