根据交换局数据制作规范规定，防套拨的原则是（）.

A、发端字冠限制，长途落地字冠限制

B、落地端位长限制，长途落地字冠限制

C、发端位长限制，长途落地字冠限制

D、发端位长限制，长途落地位长限制

Which of the following conditions is most likely to exist for a typical production process when average product is at its maximum（）

A. Marginal product is increasing.

B. Marginal product is at a minimum.

C. Average variable cost is at a minimum.