—Where the computer?
— on the teacher's desk.
A: is; Its
B:are; They are
C: is; It's
D:are; It is
条 只 口 幅
一____水井
一____图画
一____水桶
一____小溪
在一山顶有铁塔AB,从点P到铁塔底部B点有一条索道PB,索道长为300米,与水平线成角为α=30°,在P处测得A点的仰角为β=45°,试求铁塔的高AB.(精确到0.1米,其中2≈1.41,3≈1.73)
读图,回答下题.