Question

escreva as frases no past continuous= he go to school when mary arrived

Answer 1

Ele estava indo para escola, quando Mary chegou

Answer 2

Olá,

A estrutura do past continuous é:

Sujeito + verbo to be (pas. simples) + verbo principal (pres. cont.) + complemento

Presente simples:
He goes to school when mary arrived

Past continuous:
He was going to school when mary arrived

Sujeito: he
Verbo to be: was
Verbo principal: going
Complemento: to school when mary arrived

Bons estudos ;)