问题补充：
-What are you going to do this Sunday?
-I yet.
A. won decide
B. didn decide
C. haven decided
D. don decide
答案：
A. won decide
B. didn decide
(答案→)C. haven decided
D. don decide
解析：现在完成时用来表示之前已发生或完成的动作或状态，其结果的确和现在有联系。动作或状态发生在过去但它的影响现在还存在；也可表示持续到现在的动作或状态。其构成： have (has) +过去分词。根据语境可知此句的含义是我还没决定,因主语是I,故用助动词have not+过去分词,故选C.
