Forwarding is a technique used in a pipeline to reduce the number of stall cycles caused by hazards. Each sequence of instructions shown below causes a hazard for the version of the RISC-V pipeline that we studied in class. The pipeline bubble that would be caused by some of these hazards can be avoided through the use of forwarding. Others cannot. Mark the sequences for which the bubble cannot be avoided through forwarding. (_______)
A、lw x5, 0(x6) sll x9, x10, x11 add x7, x8, x5
B、add x7, x8, x9 beq x7, x0, L2
C、sub x5, x6, x7 add x8, x9, x5
D、lw x5, 0(x6) add x7, x8, x5