All four are true, technically.
But the right answer is probably the third one.
Answer:
What is the shortest sequence of MIPS instructions that extracts a field for the constant values of bits 7-21 (inclusive) from register $t0 and places it in the lower order portion of register $t3 (zero filled otherwise)? - sll$t0, $t3, 9# shift $t3 left by 9, store in $t0
srl $t0, $t0, 15# shift $t0 right by 15
Explanation:
The shortest sequence of MIPS instructions that extracts a field for the constant values of bits 7-21 (inclusive) from register $t0 and places it in the lower order portion of register $t3 (zero filled otherwise) is shown below:
sll$t0, $t3, 9# shift $t3 left by 9, store in $t0
srl $t0, $t0, 15# shift $t0 right by 15
