永信瓶盖厂加工一批瓶盖，甲组与乙组合作需要a天完成，若甲组单独完成需要b天，乙组单独完成需（ ）天。
“a+c＞b+d”是“a＞b且c＞d”的[ ]
A．必要不充分条件
B．充分不必要条件
C．充分必要条件
D．既不充分也不必要条件
His writing is so neat that it’s easy for the teacher to make out ______ he is trying to express.
A．what is it that
B．that it is what
C．that is it what
D．what it is that
