The fact that Nina says "That dog is running around" instead of "Dog that running around is" indicates an understanding of

a. holophrases.

b. syntax.

c. MLU.

d. morphemes.

correct answer is b. syntax

Explanation:

we know that Dog is endowed as a special ability for understanding human signal so when we say a dog is running around instead of the Dog that running around is

it is syntax because it is used by a non-human animal that remains a controversial issue

and syntax error is writing an arrangement of word and phase

the correct answer is b. syntax