Towards ___________ morning, _________ heavy snow began to fall.
| A．the... a | B．an... a |
| C．a...不填 | D．不填...the |
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 |