He is busy preparing a secret present for his Mum, is cheap but special.
A. one what
B. what
C. one that
D. that
网友回答
A. one what
B. what
(答案→)C. one that
D. that
解析：考查代词和定语从句：句意：他在忙着给妈妈买礼物，一个便宜但是特殊的礼物。这里如果当成非限制性定语从句，用which，不能用what或that，这里用代词指代a present做同位语，that引导的是定语从句，修饰one，选C。