Answer from cs61c-eb (Dae-Yeon Kim 16568138) for Question 3
Pipeline is stalled by having the same effect as the nop instruction.
It prevents PC register and IF/ID pipeline register from
changing, and by setting all 9 control fields in EX, MEM, WB to 0.

If (ID/EX.MemRead and ((ID/EX.RegisterRt = IF/ID.RegisterRs) or (ID/EX.RegisterRt = IF/ID.RegisterRt))), the control for the hazard detection unit will return 1, or else 0.
Then the hazard unit will send signals to PC register
and IF/ID pipeline register to do the normal pipelining.