Question

a. disconnect it from its power source
b. connect it to its power source
c. turn the chuck to insert the shank
d. tighten the chuck

Explanation:

When dealing with tools (like power tools for inserting a shank into a chuck), safety requires disconnecting from the power source first to avoid accidents. Connecting to power (B) is unsafe. Turning the chuck to insert (C) or tightening (D) should be done after disconnecting power. So the correct action before inserting the shank is disconnecting from the power source.

Answer:

A. disconnect it from its power source