Choose the sentence where climbing is used a gerund.

a. mr. herrera planted climbing ivy on the side of his house.
b. the explorers were climbing up the steeply sloping mountain.
c. the children enjoyed climbing on the playground equipment.

The correct answer is b. The explorers were climbing up the steeply sloping mountain. 

Out of all the choices, the word climbing is used as a gerund in this option: b. The explorers were climbing up the steeply sloping mountain. 
It was not used as gerund in the following: a. Mr. Herrera planted climbing ivy on the side of his house and c. The children enjoyed climbing on the playground equipment. I hope that this answer helped you.