Question

He asked doubtfully ____ who asks? Why doubtfully?

Answer 1

Answer:

The words 'your decision' which follows the blank is a noun phrase. Hence, in the phrase 'doubtful ______ your decision', the blank needs to be filled with the prepositions 'about' or 'of'. The common usage is 'doubtful about something', or 'doubtful of something'. Hence, option A is correct.

The phrases, 'doubt upon something', 'doubtful at something' and 'doubtful for something' are grammatically incorrect. Hence, options B, C and D are incorrect.