swear
1.比较下面两句：
He swore to send in his report within three days.
He swore to having sent in his report already.
第一句里的swore作“严正地允诺”解，后面接不定式，第二句里的swore to作“发誓而说”或“严正地说”解，后面接动名词。
2.下面每组里的各句意思相同：
I believe it to be true, but I cannot swear it.
I believe it to be true, but I cannot swear to it.
Can you swear that you saw him enter the house?
Can you swear to it that you saw him enter the house?
Can you swear to having seen him enter the house?
