To reach Africa we flew high mountains deep valleys and great deserts(沙漠).A. on across

问题补充：

To reach Africa, we flew high mountains, deep valleys and

great deserts(沙漠).

A. on, across, though

B. over, through, through

C. over, through, across

D. on, in, across

答案：

A. on, across, though

B. over, through, through

(答案→)C. over, through, across

D. on, in, across

解析：介词辨析。Over越过（从空中）；through穿过（从内部穿过）；across从表面越过；on在..上面；in在…里面；句意：为了到达非洲，我们飞越高山，穿过峡谷，跨越沙漠。故C正确。