A.
The children ran in every direction. They were glad to be outside.
B.
The children ran in every direction, glad to be outside.
C.
The children ran in every direction. Glad to be outside.
D.
Glad to be outside, the children ran in every direction
The answer is: C. The children ran in every direction. Glad to be outside.
The sentence fragment is "glad to be outside" because it is written as a sentence but, in fact, it is a dependent clause which can not stand alone, it requires at least one independent clause (with subject and verb such as the children ran in every direction) to be considered a sentence, or, as the other answer options illustrate, the dependent clause needs to be followed or preceded by a comma.
