Question

---The air is full of smoke and people are coughing.

---It'll get worse____the government does something about pollution.

1. A.
   but
2. B.
   unless
3. C.
   besides
4. D.
   except

Answer 1

B
unless的用法:
unless (conj. 除非) = if not; except if
(1) We are leaving now unless you want us to wait for you.
(2)【误】We'll go to Paris for our holiday, unless it isn't expensive.
【正】We'll go to Paris for our holiday,unless it is expensive.
(3)【误】You must not use my pen unless write a letter.
【正】You must not use my pen unless writing a letter.
=You must not use my pen if you are not writing the letter.
(4) Unless he starts at once, he'll be late.