Thunder occurs as ____________ through air, causing the heated air ...

★ TOEFL

Thunder occurs as ____________ through air, causing the heated air to expand and collide with layers of cooler air.

A. an electrical charge

B. passes an electrical charge

C. the passing of an electrical charge

D. an electrical charge passes

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Lapis Lazuli, ________ stone, hs been valued for ornamental purposes for more than 6000 years.

A. an opaque deep blue

B. is an opaque deep blue

C. it is an opaque deep blue

D. that is an opaque deep blue