关于duty 急急急

不正确.
Don't throw litter about .是个祈使句，不能作主语，应改为 Not throwing litter about ,用动名词作主语。

不能这样说

不乱丢垃圾是我们的责任.
It's our duty not to throw litter.

语法不对，
it's our duty not to litter.

很正确.