Help disabled people whenever you can ______ you will make the world a nicer place to live in.
A．unless B．or C．and D．but
___ that may generally reduce the amount of labor needed on construction sites by 90 percent.
A．So clever the construction robots
B．Such construction robots are clever
C．So clever are the construction robots
D．Such clever construction robots are
___ 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
