About the word "competition"

[linhtho0211]

What do you think is the mistake in the following sentence?
Some of the stiffest competitions that jackals face on the plains
of Africa comes from vultures.

The answer key is A but I think B must be competition, not competitions. Competitions in plural form only mean events which people take part in to find out who's best at a activity.
What would be the correct sentence here? Please help me.
Thanks in advance.

[linhtho0211]

But "some of competition" can also go with "comes".

[Raymott]

But "some of competition" can also go with "comes".

I'd suggest that the correct sentence is:
Some of the stiffest competition ... comes ... (as you say).

[BobK]

I'd suggest that the correct sentence is:
Some of the stiffest competition ... comes ... (as you say).

I'm afraid the other answer is just wrong. 'Competition' in this context is uncountable (the s is wrong), so 'some' is singular.

b