A. what             
B. whether           
C. that              
D. if

A: whatever
B: however
C: whoever
D: what

[     ]

A. Because
B. If
C. While
D. After

[     ]

A. until
B. though
C. if
D. and

A. Though；but
B. Though；yet
C. But; though
D. Although; but

A. that
B. when
C. whether
D. if

[     ]

A. how
B. when
C. whether
D. where

1. The old man was too tired to walk on.
  The old man was _______ tired _______ he couldn't walk on.
2. Mike is the tallest in his class.
  Mike is taller _______  ________  ________  ________ in his class.
3. I will go to bed when I finish writing the letter.
  I _______ go to bed _______ I finish writing the letter.
4. It's about half an hour's walk.
  It takes about half an hour to go there _______  ________.
5. Work hard, and you will get good marks.
  _______  _______ work hard, you'll get good marks.
6. John was busy at 9 last night.
He was writing his English composition at 9 last night.
John _______  _______  ________ his English composition at 9 last night.

A. why   
B. when 
C. how  
D. where 

A. before            
B. if                 
C. while   
D. as