Select the most appropriate set of idioms to fill in the blanks.
His offhand remarks ___________ of the members of the committee. But the Chairman told the members to ______________ and stop arguing.

Option B: Correct.

This question uses common phrases/ idioms

The right idioms used here are- ruffled the feathers, cool their heels and cool it.

Now we have to use the right combination on the basis of the sentence. 

Ruffled the feathers is appropriate for the first blank because it means "to annoy" or "upset".

Cool their heels means to wait for a significant amount of time, mostly for someone else, therefore cool their heels is a misfit here, since the members are likely being asked to calm down and not wait.

Cool it means to calm down and hence it is the right choice.