Question about wording of problem geometry

[Taylor_1989]

So I am not asking for any help, on the question, I figured it out and got the right ans. My problem is with the wording.

Question: The points A,B and C lie on Horizontal ground and are such AB=19m, BC=16m and CA=21m

a) calculate the size of angle ACB

The part I have underlined is the bit that through, a bit confusing mainly because I can't really picture it, dose it mean that is lie in the horizontal plane, or something like that. The only way I was able to workout that, I had to use the cosine rule was because it ask me to calculate the size of angle ACB. So basically I made a assumption, which is not good, when trying to figure out maths.

Could someone help me out with the wording of the question, to me its slightly misleading.

Thanks in advance; happy new year.

 

[haruspex]

Yes, it just means they're in a horizontal plane. Seems like an attempt to use less technical language.