Answer from cs61c-es (Meng Chang Bruce Lin 16075852) for Question 2
PC-relative addressing refers when the program counter banches address to nearby locations to fulfill necessary size for address field. For instance, in J type format, 26 bits are for address field and 6 bits are for operation field.
For the code above, it probably will not work since in 
HERE: if $t1, $t2 are equal, we will branch to THERE:
, but in THERE: we add $t2 and $t3, store the result in $t1. In another word, we are incrementing $t1. But, then if we go back to HERE: again somewhere in the code, we will find that we might not be able to branch back to THERE:.