C, D, the overall stress analysis and weight of the balloon, gravity (M+m)g, buoyancy F floating, supporting force N, wind force F and friction force F, according to the balance conditions, are as follows:

N=(M+m)g-F float ①

f=F ②

From the formula (1), it can be seen that the supporting force of the ground to heavy objects remains unchanged, so c is correct;

According to formula (2), the friction between the ground and the heavy object changes with the change of wind, so d is wrong;

A, B, balloon stress analysis, under the action of gravity, buoyancy, thin wire tension and horizontal wind, as shown in the figure, according to the balance conditions, there are:

Tsinθ=F

F floating -Tcosθ-mg=0

Solution:

T=F2+(F floating? mg)2？ ③

Tanθ=FF floating? Mg? ④

According to Formula ③, the pulling force increases with the increase of wind power, and the pulling force of the thin wire on the object is equal to the pulling force of the thin wire on the balloon, so B is wrong;

According to formula (4), the angle between chord and vertical direction increases with the increase of wind force, so A is wrong;

So choose: C.