For question number 12-5. why can't the answer be D)it may be either at rest or moving in constant velocity?

I understand that when net Force is 0, that doesn't mean it isn't moving so it can't be A). But when the net Force is zero. doesn't that only mean the acceleration is zero? If so, wouldn't it give the chance of both rest and constant velocity as an answer? 

I'm not sure why rest can't be part of the answer..

Thank you for helping!!