下列各图象能正确反映所对应的实验事实的是

A． 充分加热等质量的氯酸钾制氧气

B． 往稀硫酸中加入氯化钡溶液至过量

C． 滴加稀盐酸恰好中和pH=13的氢氧化钾溶液

D． t℃向某接近饱和的硫酸钠溶液中缓慢加入硫酸钠粉末（a%为该溶液溶质质量分数）

The major problem with E-mail is that it is (71) easy to use that people can become (72) with messages (73) they can possibly answer in a day. In addition, mail boxes require some management to (74) messages or archive those that might be required later. Senders don’t always know about your E-mail backlog and often send (75) messages.

A．more than

B．than

C．that

D．which