'There is smoke on the distant hill. Since smoke is always accompanied by fire, the hill must have fire too.' Which of the following corresponds to the middle term (hetu) in the above argument?

In the smoke-and-fire inference the reason-mark (hetu, the middle term) is the smoke.

The hetu is the sign present in the subject (paksha) that leads to the probandum.

Here smoke is seen on the hill and is invariably tied to fire.

Fire is the major term (sadhya) inferred, and the hill is the minor term (paksha).

So the middle term that mediates the inference is smoke.