A and B "is" (not "are")?

This is an article from BBC News.
BBC News - Coronavirus: Sars-like virus death reported in UK

Coronavirus: Sars-like virus death reported in UK

A patient infected with a new respiratory illness similar to the deadly Sars virus has died in the UK.
(omitted)
The exact source of the new virus and how it spreads is still unknown. The leading theory is that it comes from animals and the new Sars-like virus does appear to be closely related to a virus in bats.

I have a question about the blue sentence. Shouldn't it be "are" instead of "is"?
I think the sentence says that two things ("the exact sources of the new virus" and "how it spreads") are unknown.

Quote:

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Originally Posted by pinkie9

This is an article from BBC News.
BBC News - Coronavirus: Sars-like virus death reported in UK

Coronavirus: Sars-like virus death reported in UK

A patient infected with a new respiratory illness similar to the deadly Sars virus has died in the UK.
(omitted)
The exact source of the new virus and how it spreads is still unknown. The leading theory is that it comes from animals and the new Sars-like virus does appear to be closely related to a virus in bats.

I have a question about the blue sentence. Shouldn't it be "are" instead of "is"?
I think the sentence says that two things ("the exact sources of the new virus" and "how it spreads") are unknown.

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It's fine with "is".

Could anyone please tell me why?

Quote:

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Originally Posted by pinkie9

Could anyone please tell me why?

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Because "the exact sources of the new virus" and "how it spreads" are considered to be one thing?
To me, it seems to be two things. :-|

Also, would it be incorrect if "are" was used here?

I would use "are." It's two things to me.

So...is it a difference between BrE and AmE?