Answer

Correct Answer is a.(spikes)

Explanation:

option a is correct because here serves, rotation and spikes all the three words are using as object.

The volleyball team practiced their serves, rotations, and spikes.

option b cannot be correct because here spiking is used as a verb and sentence(The volleyball team practiced their serves, ) is in past indefinite form and we cant use word spiking here because this form of verb is used in continues form of sentences only.

Option c cannot be correct as because in this option “”spikes the ball” spikes is used as a verb  which can be used in present indefinite form of sentence only but here sentence is in past indefinite form.

Again option d cannot be correct because  in this option “”spikes over the net” spikes is used as a verb  which can be used in present indefinite form of sentence only but here sentence is in past indefinite form.