Everyone in this country should work hard and do what they can _____ against national smog.
| A．fight | B．fought | C．fighting | D．to fight |
________ you’ve got two film tickets, you may as well invite Mary to go with you tonight.
A Now that B After all C Although D As soon as
In time of serious accidents，____we know some basic things about first aid，we can save lives.
A whether B. until C. if D unless
He tried his best to solve the problem，_____difficult it was.
A however B. no matter C. whatever D. although
Parents should take seriously their children's requests for sunglasses ____eye protection is necessary in sunny weather.
A because B. though C. unless D. if
Roses need special care ____they can live through winter.
A because B. so that C. even if D. as