Answer from cs61c-cb (minh uyen nguyen 16765774) for Question 1
MIPS software places an instruction immediately after the delayed branch instruction that is not affected by this branch.  
For example, if there is an instruction right before the branch instruction and it is not affected by the branch instruction, then we can move that instruction to be right after the branch instruction.  And that position right after the branch instruction is called a branch delay slot.  
Its purpose is to solve the control harzard problem.