In chair cyclohexane, the steric hindrance of the flat substituent is less than that of the upright substituent, so it is more stable.

For disubstituted cyclohexane, it is the most stable when both groups are in plane position. If one group is in an upright position, the smaller group has less steric hindrance when standing upright, so it is more stable.

So question 2 should be C.

Question 44: For monosubstituted cyclohexane, the chair conformation is more stable than the boat conformation unless the substituent is particularly large (even if the substituent is in the upright position), so C and D are excluded first. Among A and B, B with methyl group in the horizontal position is more stable, so B is selected.