超声波的频率为()
A.<16Hz
B.16~2×10 4Hz
C.2×10 4~2×10 8Hz
D.10 8~10 10Hz
E.>10 10
参考答案:C
On the bank of the river, we found him _____on a bench, with his eyes _____on a kite in the sky.
A.seated; fixing
B.sitting; fixing
C.seated; being fixed
D.sitting; fixed
下列危险化学品中,其燃点最低的是( )。
A.乙醇
B.汽油
C.氨
D.硫化氢