Unionized Employees of Serve-Me Company Vote to Strike

Unionized employees of Serve-Me Company vote to strike.They decide,however,that instead of actually leaving the premises,they will simply do no work.Which of the following is true?

A) Remaining at work, but performing no work, is a valid and legal form of a strike.
B) Remaining at work, but performing no work, is an illegal wildcat strike.
C) Remaining at work, but performing no work, is an illegal sit-down strike.
D) Remaining at work, but performing no work, is an illegal partial strike.
E) Remaining at work, but performing no work, is a valid and legal form of a strike, but only if the employer has threatened to hire replacement workers.