Answer from cs61c-aw (wing hin kao 16500429) for Question 2
They all come from EX stage, MEM stage and WB stage.
add $1, $1, $2
add $1, $1, $3 ---MEM forward $1

lw $1, 0($sp)
add $2, $3, $4
addi  $5, $1, 1 ---WB forward with $1

add $1, $0, $2
add $5, $4, $3 ----ID forward with $4, $3