∴∠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.