问题
选择题
Eco-travel is a form of travel _____ combines normal tourism with learning, _____ a way to find out what
can be done to help animals, plants and people. [ ]
A. what; as well as
B. that; as well
C. which; as well as
D. which; as well
答案
答案：C
所占的物质的量分数为____。