______ there are living creatures in the outer space as those on Earth hasn’t been proved so far.
| A．When | B．How | C．If | D．Whether |
相关试题
Without the 
air to hold some of the sun’s heat, the earth at night ____ for us to live.
| A．would be freezing cold | B．will be freezing coldly |
| C．would be frozen cold | D．can freeze coldly |
It is hard for me to imagine what I would be doing today if I ____ in love, at the age of seven, with the Melinda Cox Library in my hometown.
| A．wouldn’t have fallen | B．had not fallen |
| C．should fall | D．were to fall |
“Do you know his address？” “No, I also wish I _____ where he _____.”
| A．knew, live | B．knew, lives | C．know, lives | D．know, lived |
“I still haven’t thanked Aunt Lucy for her present.” “It’s time you _____.”
| A．do | B．did | C．had | D．would |
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