问几道英语题目,讲下原因1.A thief got into the old man's house because h

问几道英语题目,讲下原因
1.A thief got into the old man's house because he forgot ___the window yesterday.
我觉得是A但答案是C
A.to close B.close C.closing D.closed
2.It is __for us to travel more quickly than before because we have high-speed trains.
为什么是B
A.easy B.easier C.easiest D.the easiest
3.Peter__to work in his homework after her,graduated from Har-vard University A.goes B.went C.will go D.had gone