Conjunctions using   because
The dog bit John.  He was teasing it. We can join these sentences by using  because. Because  is a conjunction.
The dog bit John  because   he was teasing it.
Tom was very happy.  He was on holiday.
Tom was very happy  because  he was on holiday.
She didn’t drink the tea.  It was very hot.
She didn’t drink the tea  because  it was very hot.
Elsa went to bed.  She was feeling ill.
Elsa went to bed  because   she was feeling ill.
I missed the bus.  I was late.
I missed the bus  because   I was late.
I didn’t buy the hat.  It was very expensive.
I didn’t buy the hat  because   it was very expensive.

Conjunctions: 'because'