Correct : c

The correct answer is Option C: B4 = {g*k}, B5 = {c+m}.
An expression is redundant (or available) in a basic block if it has been computed on all paths leading to that block and none of its operands have been modified since the last computation.
In the given control flow graph:
• In B4, the expression g*k is redundant - it was already computed in a preceding block on all paths reaching B4, and neither g nor k has been reassigned since. So g*k need not be recomputed.
• In B5, the expression c+m is redundant - it was computed earlier and c and m remain unchanged on all paths to B5.
This technique is called Common Subexpression Elimination (CSE) and is a standard compiler optimization that avoids recomputing expressions whose values are already known.