We turn off the light when we leave the room to protect the environment .
=We turn off the light when we leave the room so that we can protect the environment .
to do sth
= in order to do sth
=so that +从句
We turn off the light when we leave the room to protect the environment .
=We turn off the light when we leave the room so that we can protect the environment .
to do sth
= in order to do sth
=so that +从句