根据《农用地定级规程》的规定，修正法定级是在农用地分等指数的基础上，根据定级目的，选择（）等因素计算修正系数，对分等成果进行修正，评估出农用地级别的方法。

A．自然因素、区位因素

B．区位因素、社会因素

C．自然因素、区位因素、社会因素

D．区位条件、耕作便利度

(41) is a protocol that a host uses to inform a router when it joins or leaves an Internet multicast group.
(42) is an error detection code that most data communication networks use.
(43) is an interior gateway protocol that uses a distance vector algorithm to propagate routing information.
(44) is a transfer mode in which all types of information are organized into fixed form cells on an asynchronous or non-periodic basis over a range of media.
(45) is an identifier of a web page.

A．4B/5B

B．CRC

C．Manchester Code

D．Huffman Code