Steve's activity on Sunday
In the past
He spent most of the time 1.
He learnt it from his 2 and he is good at it.
Now
He spends at least 3 hours collecting rubbish.
He would like to protect the beach.
在△ABC中，A:B:C=1:2:3，则a:b:c=（ ）
长江上游地区主要的生态环境问题是（ ）
