Here are the correct options for each statement:

1. **We should walk to school,** **so** **we shouldn’t throw trash on the ground.**
2. **We should recycle at home** **so that** **we can reduce land pollution.**
3. **We should turn off air conditioners when we leave a room,** **and** **we should ride bicycles.**
4. **We should reuse plastic bags** **so that** **we don’t need to throw so many in the trash bin.**
5. **We shouldn’t throw trash in the sea,** **and** **we should help clean up beaches.**

So the correct options are:

1. so
2. so that
3. and
4. so that
5. and