Crew of Dutch explorer Abel Tasman
Some experts regard heroin as the most addictive drug available on the street, but many research scientists have questioned this assumption in recent years. Even though heroin is famous for it's addictiveness, recent studies pointed that it can vary depending on the mode of use they employed.
The correct answer is was working.
You need to use past continuous tense (was working) to denote that an action which was being processed for a period of time has now been interrupted. So, Penelope was working on her homework for a prolonged period of time, and then the doorbell rang and interrupted her.
The answer is... C) orally
