Destruction of the environment is one of the most serious ___ we face.
A. predictions
B. challenges
C. operations
D. combinations
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I’m busy on Monday. ___ having that game on the weekend?
A. How come
B. How often
C. How about
D. How long
Most parents have no time to ___ their children.
A. command
B. control
C. dominate
D. tutor
___, your child will leave home to lead her own life as a fully independent adult.
A. Scarcely
B. Occasionally
C. Seldomly
D. Eventually
Dogs hear far better than human beings do. They are able to hear high ___ that humans cannot hear.
A. variations
B. channels
C. frequencies
D. repetitions