With Respect to Long- Run Economic Growth, One Rationale for the Idea

With respect to long- run economic growth, one rationale for the idea that there may be increasing marginal returns to investment is that

A) as further investment takes place the economy moves down to the right along the marginal product schedule.
B) as further investment takes place the economy moves upward to the left along the marginal product schedule.
C) initial investment shifts the the investment demand schedule to the left, making further investment less costly.
D) the investment costs to "followers" are lower than those for "pioneers".
E) initial investment shifts the the aggregate demand schedule to the left, making further investment less costly.