He used ... A lot when he in the country 1. Swam 2. to swim 3. swim 4. swimming

1) He used to swim a lot when he lived in the country.

We used the expression 'used to' to denote a habit, frequent action in the past. This expression is never used for present habitual actions but only for regular actions in the past. NB: don't mix up the expressions 'used to' do something and 'to be used to' doing something'. They have completely different meaning, though they may seem similar to you.