Scraping oneself on a contaminated object may cause infection.
An infection is an invasion of the body by bacteria.
Scraping oneself on a contaminated object may cause an invasion of the body by bacteria.
Scraping oneself on an object that is what, may cause an invasion of the body by bacteria?

[A] unknown
[B] safe
[C] threatened
[D] harmful substances
[E] Pollution
[F] foreign
[G] barrel-shaped
[H] contaminated