Maryna is interested...reading books.
Ivan in keen... writing messages.
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Maryna is interested in reading books.

Ivan is keen on writing messages.

1.i was having a stroll when i saw a car accident 2. when   dad   entered the room   mother was singing а lullaby. 3. she sat down on а chair while he was painting her portrait. 4. when   we / сотеd   from the party   he was listening to   one of his records.

let’s meet outside the sport centre.-давайте встретимся вне спортивного центра. 

а.that’s kind of them.-это - вид их.

b.just a moment.-только момент.

c. i might be a bit late.-я мог бы немного опоздать.

соответсвенно ответ будет c))