but that explanation raises another question. 但这里又牵扯出另一个问题

135. They're very good at conserving moisture
     它们非常善于保存水分
136. but they nonetheless need a regular supply of water.
     但它们仍须定期补充水
137. They get it partly from cactus flowers
     其中一部分水取自仙人掌花
138. but that explanation raises another question.
     但这里又牵扯出另一个问题
139. How do the cacti survive without rain?
     仙人掌为何能在这个无雨地带生存
140. Hot winds suck all the moisture from the surface of the land.
     热浪抽干了地面上所有的水分
141. Clearly there must be something else that takes the place of rain.
     显然 这里必须有其它东西 能代替雨水的作用

来自《行星地球 第一季 第五集 Planet Earth S01E05 沙漠》第 138 行