They were walking a forest after they swam the river .
A. through, cross
B. across ,through
C. through, across
D. across, across
网友回答
A. through, cross
B. across ,through
(答案→)C. through, across
D. across, across
解析：through通过，强调从内部通过；cross交叉的，相反的，不能用作介词；across穿过，横穿。句意：在他们游过这条河后，他们正在穿过一座森林。前文从森林内部通过，下文从河面穿过，故选C。