(D) Alluvial soil
Alluvial soil is the most widely spread and important soil; the northern plains are made of it, and it consists of various proportions of sand, silt and clay.
All three characteristics directly match the description of Alluvial soil given in the textbook. Examiners expect you to pick the option that matches all given clues — "widely spread," "northern plains," and "sand, silt and clay" are the key identifiers of alluvial soil. Remember: Black soil = Deccan trap/cotton; Laterite = leaching/monsoon; Yellow/Red soil = Deccan plateau igneous rocks.