5. You know swimming against the current is difficult.
你知道的，逆水游泳很難。
還能這樣說：
Swimming against the current is rather hard, you know it.
As you know that it is difficult to swim against the current.
應用解析：
make against 有害，不利于；
knock up against 偶然碰見；
over against 在……對面；與……成鮮明的對比
6. Swimming in the sea is great fun.
在海里游泳很好玩。
還能這樣說：
It is full of fun to swim in the sea.
Swimming in the ocean is a lot of fun.
應用解析：
fun and games 玩耍；
just for fun 取樂；當笑話；
poke fun at 開玩笑；嘲笑；
in fun 開玩笑，不是認真的
7. Please watch your step.
請注意腳下。
還能這樣說：
Please mind the step!
Please pay attention to the ground.
應用解析：
in the night watches 晚上焦慮不眠的時候；
watch and ward 值班，看守；照料；
watch for 等待；當心；
watch out 當心，提防；注意
8. Did you go for a swim in the indoor swimming pool?
你們去游泳館游泳了？
還能這樣說：
Had you gone to the indoor swimming pool for swim?
Could you tell me if you had gone to swim in the indoor swimming pool?
應用解析：
open air swimming pool 露天游泳池；
solar heated swimming pool 太陽能游泳池；
dirty pool 不道德的行為；欺騙的伎倆