he teacher told them since light ________ (travel) faster than sound,lightning ________ (appear) to go before thunder.
travels, appears
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Onlywhenyouhaveobtainedsufficientdata________cometoasoundconclusion.
________ (fail) several times, they need some encouragement.
Wood does not conduct electricity; ________.
Howlong________they________(dig)theditch?
Herefusedtotelluswhetherhe________(undertake)thejob.
