Topics: TOEFL
The upper levels of the sun’s atmosphere are of very low ______ heats the gases there to very high temperatures.
A. dense and solar
B. density, solar activity
C. density, but solar activity
D. density and the activity of the sun is
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Only when air and water seep through its outer coat ___________.
A. does a seed germinate
B. to the germination of a seed
C. a seed germinates
D. for a seed to germinate