I tried to work on, but I was so tired that I could no longer _____ .
| A．bear out | B．hold on | C．hold up | D．work out |
___ most of the earth’s surface is covered by water, fresh water is very rare and precious.
| A．As | B．Although | C．If | D．Once |
Helen was much kinder to her youngest son than to the others, ______, of course, made the others envy him.
| A．who | B．which | C．what | D．that |
_____to reach them on the phone, we sent an email instead.
| A．Fail | B．Failed | C．To fail | D．Having failed |
He let me repeat his instructions_____ sure that I understood what was _____ after he went away.
| A．to make; to be done | B．making; doing | C．to make; to do | D．making; to do |
— It’s the classroom! So you ______ know eating is not allowed here.
— Oh, sorry.
| A．need | B．will | C．may | D．must |