He was asked to accelerate the pace of work.

Answer: Option C

Accelerate : (especially of a vehicle) begin to move more quickly.
Check : examine (something) in order to determine its accuracy, quality, or condition, or to detect the presence of something.
Control : the power to influence or direct people's behaviour or the course of events.
Slacken : reduce or decrease in speed or intensity.
Supervise : observe and direct the execution of (a task or activity).

Antonym of Accelerate is Slacken