6229 - Intermediate\Upper-Intermediate Test:4 - Radio waves ______ by the ionosphere. This makes it possible ______ short-wave radio signals over great distances.

Radio waves ______ by the ionosphere. This makes it possible ______
short-wave radio signals over great distances.
are reflecting / sent
are reflected / to send
are reflected / sending
is reflected / to send
Elementary Grammar Exercises A1
Advanced Grammar Exercises
Upper-Intermediate Grammar Exercises
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