We do not use the present progressive to talk about 'general time'. For this, we use the simple present. Compare:

• My sister's living at home for the moment, (around now) You live in North London, don't you? (general time)
  
• Why is that girl standing on the table? Chetford Castle stands on a hill outside the town.
  
• The leaves are going brown.
  
• I go to the mountains about twice a year.
  

We often use the present progressive to talk about the future.

• What are you doing tomorrow evening?

Some verbs are not used in progressive forms.

• I like this wine. (NOT I'm liking . . .)

Verbs that refer to physical feelings (for example feel, hurt, ache) can be used in the simple present or present progressive without much difference of meaning.

• How do you feel? OR How are you feeling?

• My head aches OR My head is aching

The difference between across and through is like the difference between on and in. Across is used for a movement on a surface. Through is used for a movement in a three-dimensional space, with things on all sides. Compare:

• We walked across the ice    We drove across the desert.
• I walked through the wood.    We drove through several towns.

People swim, and ships move, across rivers, lakes etc.
The river's too wide to swim across

Ladies and Gentlemen!
Here's an excerpt from the official records made at the Great Planetary Educational Convention between the Earth and the planet Q12, which is 250 million light-years away from us, to the North of the Milky Way.

The Deligate1: Hi! I am Jomeons from the Q12. You can call me lames. I will be talking about eating habits and food situation on our planet, because, as far as I know, this holds importance for the Earth people. A few facts.