Answer from cs61c-ev (Roland Carlos 16583196) for Question 2
The three values are coming from the register file, a prior ALU result, or data memory/an earlier ALU result.

register file value:

add $1, $2, $3 (where $2 or $3 do not cause data hazards).

prior ALU result:

sub $2, $1, $3
and $12, $2, $5

data memory/earlier ALU result:

add $1, $1, $2
add $1, $1, $3
add $1, $1, $4