Step 1: Understand each term.
Knot is a unit used to measure speed, especially of ships and aircraft
Watt is a unit of power
Fathom is a unit of depth or length, especially used at sea
Step 2: Find the common feature.
All three words represent units of measurement
Although knot and fathom are commonly associated with sailors, watt is a general scientific unit, so option (3) cannot include all three properly
Step 3: Conclusion.
Hence, the common relationship is that they are units of measurement