Future Employee Labor and concurrent I-140 and I-485 Job Change

[econnect]

I work for Company A
Company B has filed I-140 and I-485 recently with name change on pre-approved labor (as a future employee)

Now my questions are

A. Do I need to work for Company B which has filed my I-140 and I-485 after I get EAD(I-485) approval
B. If I need to work for Company B after EAD(I-485) approval, how long do I need to work for Company B before I take up other job
C. Can I shift my job from Company A to Company C while my I-140/EAD(I-485) approval is pending.