某金矿公司预计3个月后将出售黄金，故先卖出黄金期货，价格为298美元，出售黄金时的市价为308美元，同时以311美元回补黄金期货，其有效黄金售价为（）。

A.308美元

B.321美元

C.295美元

D.301美元

In contrast to the new teachers, the middle-standing and veteran teachers seem to have made a remarkable improvement in their ability to ______.

A．be fair to any pupil

B．evaluate pupils' progress

C．present materials clearly

D．understand and play with pupils