Isoquants Are Usually Drawn Convex When Viewed from the Origin

Multiple Choice

Isoquants are usually drawn convex when viewed from the origin, reflecting the standard assumption

A) that both factors are subject to the law of diminishing returns.
B) that the variable factor is subject to the law of diminishing returns.
C) that both factors are subject to increasing returns.
D) negative marginal productivity of all factors.
E) the positive marginal productivity of all factors.