Ploughing as an agricultural technique was practised in Harappan Civilization.

Which one of the following is NOT the evidence to prove the above statement?

Motifs of the plough displayed on the seals have been found

On the seals of the Harappan civilization, numerous motifs are found like bull, elephant, etc., but not of the plough.

While the prevalence of agriculture is indicated by finds of grain, it is more difficult to reconstruct actual agricultural practices of Harappan Civilization.
Representations on seals and terracotta sculpture indicate that the bull was known, and archaeologists extrapolate from this that oxen were used for ploughing.
Moreover, terracotta models of the plough have been found at sites in Cholistan and at Banawali (Haryana).
Archaeologists have also found evidence of a ploughed field at Kalibangan (Rajasthan), associated with Early Harappan levels.
The field had two sets of furrows at right angles to each other, suggesting that two different crops were grown together.