Answer from cs61c-ep (Hao Wen Vivian Chong 15826235) for Question 2
Because lw is the critical path in the datapath, we'd have to wait until the very end of the instruction when 0($s1) is written into $t0 before we can execute the next instruction. To reduce the performance penalty, we can insert other instructions into the datapath while we are waiting for $t0 to come out, as long as they do not affect the load word.