At college, Barack Obama didn’t know that he__________the first

2015年高考陕西卷英语试题及答案At college, Barack Obama didn’t know that he__________the first black president of the United States of America.A. was to become B. becomes C. is to become D. became

参考答案：
A 一个是虚拟，一个是要与主句时态一致。