Потому что он один из группы иностранцев, можно сказать "принадлежит к иностранцам". Тогда ставим а. Или она- доктор. She's a doctor. Или он -католик. He's a Catholic.
Hi Eric,
I'm writing this postcard on the beach.
It's a beautiful day and I'm listening to music.
I come to the beach every day.
I usually play beach and go swimming in the sea with my dad.
My mum doesn't like sitting in the sun.
She's sitting under a beach umbrella now.
See you soon.
Rich
He is jumping
They are swimming
l am love
l am washins
He wants
Where doese she work
wat are you sad
How old are you
why is your house green
What are you