Answer:
Yes, childhood is a common noun, have a nice day.
Explanation:
Arduous means<u>: involving or requiring strenuous effort; difficult and tiring</u>
Hope this helps have a great day:)
She <span>had been working</span> on the project for 2 days before she finished it. So B is the only right one as it's a continuous action before an action with an exact defining past perfect continuous. Also there's a key word "for" that can help us to find out the tense.
