5. If he (to become) a musician, his parents (to be) happy.

Решение:

Это условное предложение 2-го типа, которое описывает гипотетическую ситуацию в настоящем. Используем Past Simple в первой части и 'would + инфинитив' во второй.

1. If he became a musician, his parents would be happy.

Ответ: If he became a musician, his parents would be happy.