邮政营业部门的安全保密规定，信筒信箱按时开取邮件，开箱（）由专人保管，不得随意悬挂放置。
A.钥匙
B.信兜
C.信袋
D.工具
参考答案：A
The world’s population has grown by ______ it was in 1800.
A．more than six times that
B．six times more than that
C．more than six times what
D．six times as many as
下列各项费用中属于内部故障成本的是（）
A.降价费
B.工序控制费
C.不合格品处理费
D.进货测试费
