When an infant progresses from crawling to walking an advancement in the infant's has occurred.
a. gross motor skills
b. simple motor skills
c. complex motor skills
d. fine motor skills

The answer for your question would be : A. Gross motor skills

Gross motor skill utilize the movement from one's arms, leg, and feet to create a larger actions such as walking, jumping , or running. The fact that that infant are capable to walk is a sign of the development of Gross motor skills

The answer to your question is Gross motor skills - a.

The reason for this is the following, when an infant advances from crawling to walking, he's changing the qualitative pattern of movement that he is able to do, with this he changes essentially his ability to move around in the world. Such qualitative patterns of movement are also often depicted as gross motor skills. 

Ibelieve the answer to this question is a