---How did it that all the flowers died ?-I had forgotten to water them.A. come onB. c

问题补充：

---How did it that all the flowers died ?

---I had forgotten to water them.

A. come on

B. come up

C. come about

D. come along

答案：

A. come on

B. come up

(答案→)C. come about

D. come along

解析：本题的含义是所有的花都死了是如何发生的，我忘记给它们浇水了，come about表示发生的意思，与本题的意思相符，故本题选C。