M点高程HM=43.251m，测得后视读数a=1.000m，前视读数b=2.283m。则N点对M点的高差hMN和待求点N的高程HN分别为：
A.1. 283m ,44. 534m
B.-3. 283m,39. 968m
C.3. 283m ,46. 534m
D.-1. 283m,41. 968m
正确答案是D