Concept:
Different variants of the Knapsack Problem can be solved using different algorithmic strategies.
Common strategies include:
• Greedy Method
• Dynamic Programming
• Backtracking
• Branch and Bound
These approaches are used depending upon whether the problem is fractional, 0/1, bounded or unbounded.
Step 1: Fractional Knapsack.
Fractional Knapsack is optimally solved using the
\[
\text{Greedy Method}.
\]
Step 2: 0/1 Knapsack.
0/1 Knapsack can be solved using
\[
\text{Dynamic Programming}.
\]
Step 3: Optimization approaches.
Backtracking and Branch-and-Bound are also widely used for knapsack variants.
Step 4: Identify the correct option.
Hence all four strategies are applicable.
Therefore,
\[
\boxed{\text{a,b,c,d only}}
\]
is the correct answer.