Yes, and that is sometimes something that that the speaker decides at the moment of speaking. For example, swimming and mountain-climbing are clearly two different activities, but running and throwing balls might be thought of by some children as one activity.So, the issue is whether it's considered one or two activities.
I agree that it's not very likely, which is why I used 'are' in my first response. However, I have seen children in twos and threes running around and passing/throwing a ball to each other. I think it's just about possible they might think of 'running and throwing balls' as one activity.I can see running and jumping as one thing. I can't see those two as one thing.
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