Question 15: Mark the letter A, B, C, or D on your answer sheet to indicate the undelined part that needs correction in each of the following questions: The new technique calls (A) for heat (B) the mixture before applying it (C) to the wood. (D)
We have: After the preposition is V-ing. So: heat => heating.
The new technique requires heating the mixture before joining it to the wood.
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