Up to 150 workers were believed to have been inside the factory, which produces syringes and other plastic medical supplies, at the time of the explosion.

Choose your answer: based on the paragraph above can we conclude that "The explosion did not happen when the plant was empty but when employees were there."?

Options are:
[a]. Yes;
[b]. It's impossible to say;
[c]. No;
I think the answer is
[a].