What does compulsion mean as it is used by Ismene in lines 63-66?

Therefore I plead compulsion and entreat
The dead to pardon. I perforce obey
The powers that be. 'Tis foolishness, I ween,
To overstep in aught the golden mean.
Answer choices for the above question

A. An inability to make a decision

B. A refusal to do what is required

C. A duty to act according to the law

D. n acknowledgement of uncertainty