When does a soft blend form between watercolours?

Correct answer: When colours meet on a wet surface

A soft blend is produced by the wet-on-wet method. When the paper or an existing colour area is still damp, fresh watercolour moves gradually into it and the boundary becomes gentle rather than sharp, so option B is correct. Dry paper tends to preserve harder edges, oil interferes with absorption, and a thick layer does not by itself create a soft transition.