两道 英语语法题~~~~~o(^▽^)o 求解

Since food security guaranteed the peple to have enough food to maintain a normal physiological life, it was essential that the country or region______ an adequate food supply to meet its residents' demand for food.

A.has

B. had

C.having

D.have (答案D,不应该是过去式吗，或者即使是现在时，不是用or的就近原则吗？）

We stayed at work until 8pm tonight trying to figure out how to explain the financial market, and we went home ______.

A.to be exhausting

B.being exhausted

C.exhausting

D.exhausted（答案D，为什么不选B呢？）

万分感谢，求解。。。