【单选题】
They marched through the square,in the middle of [填空]stood a monument.
【单选题】
It was required that the crops [填空] harvested at once.
【单选题】
Shes determined [填空] there
【单选题】
She came in, a baby[填空] in her arms.
【单选题】
I am[填空]?tired?that I don’t want to go out.
【单选题】
It was not until his wife came back [填空]he went to bed.
【单选题】
He was[填空]excited?that he could not speak.
【单选题】
Only in this way [填空]we learn English well.
【简答题】
一个代数系统中,逆元的存在性是怎样的?