The city park will be cleaner ___________ people stop dropping litter here and there. 
#56719
A
while
B
if
C
unless
D
before
推荐题目
My father feels ________ because he heard from ________ today. 
#58571
A
happy;an old friend of he
B
happy;an old friend of his
C
happily;one of his old friends
D
happily;an old friend of him
_____ he was tired , ____ he didn’t stop working .
#57240
A
Although ; but
B
Though; /
C
But ; /
D
Though ; but