Answer:
b. lw $t4, 4($t0)
c. add $t3, $t5, $t4
Explanation:
Pipeline hazard prevents other instruction from execution while one instruction is already in process. There is pipeline bubbles through which there is break in the structural hazard which preclude data. It helps to stop fetching any new instruction during clock cycle.
System crashes, viruses and fragmented file systems are hallmarks of Windows systems, but your teacher is probably looking for Hard Drive for the answer.