Resposta:
a) Mary IS at school. (INCORRETA)
b) Peter is alone today. (CORRETA)
c) My family IS working now. (INCORRETA)
d) My friends ARE living in São Paulo. (INCORRETA)
e) My teacher IS buying a new house. (CORRETA)
f) I AM happy today. (INCORRETA)
g) My brother IS sad today. (INCORRETA)
h) My dog IS angry. (INCORRETA)
i) They ARE hungry. (INCORRETA)
j) My uncle is a doctor. (CORRETA)
Explicação passo-a-passo: