∫ The diameter of the balloon is 4m, the radius is 2m, and the measured viewing angle of the balloon is ∠ BAC = 2 (AB and AC are tangents of ⊙O, and B and C are tangents).

∴∠OAC= 1，

In Rt△OAC, OC=2m, ∠ OAC = 1,

∫sin 1 = OCAO，

∴ao=20.0 175= 1 14.2(m).

In Rt△OAD, there is OD = OA× SIN 60 ≈ 99 (m).

A: The height OD of the balloon center from the ground is about 99 meters. ..