下列表示测流方法的符号中，（）代表用水力学法推算的或上年末、下年初的接头点据。
A、O
B、∨
C、Δ
D、×
参考答案：D
Sometimes they may play to passers-by in the street or subway so that they can earn some______ money for themselves or to pay for their instruments.
A．certain
B．extra
C．various
D．unusual
普通型带式输送机倾斜角度不允许超过（）。
A.18°
B.4°
C.20°
