Up till now we _______ four units and this will be the second time that we _______ a test.

A．have finished; have had

B．finished; will have

C．have finished; are to have

D．will finish; have had

飞机在航线飞行时进入层云和层积云，可能碰到的积冰情况是（）.

A.冻结迅速的明冰

B.弱积冰或中度积冰，且云的上部积冰比下部要强

C.一般为中度积冰，且云的下部积冰比上部要强