Which of the following factors are taken into account for estimating the runway length required for aircraft landing ?

1. Normal maximum temperature
2. Airport elevation
3. Maximum landing weight
4. Effective runway gradient
Select the correct answer using the codes given below Codes?
A. 1,2,3 and 4
B. 1,3, and 4
C. 2 and 3
D. 1,2 and 4