∴∠ACB=∠CBD-∠A=60 -30 =30，

∴∠A=∠ACB，

∴BC=AB= 10 (meter).

△BCD, CD=BC in a right angle? Sin ∠ CBD =10× 32 = 53 ≈ 5×1.732 = 8.7 (m).

A: The height of this tree CD is 8.7 meters.