Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: Centrioles are rod-like structures made of short microtubules. Nine groups of three microtubules make up each centriole. Two perpendicular centrioles make up the centrosome . Centrioles are very important in cellular division, where they arrange the mitotic spindles that pull the chromosome apart during mitosis. Answer: centrioles
[A]: What are the rod-like structures made of short microtubules that play an important part in cellular division?

[Q]: Passage: Immovable joints do not allow the bones to move at all. In these joints, the bones are fused together by very tough collagen. Examples of immovable joints include the joints between bones of the skull. You can see them in Figure below . Answer: immovable joints
[A]: The joints that are between the bones that make up the skull are what kind of joints?

[Q]: Passage: Calculating acceleration is complicated if both speed and direction are changing. It's easier to calculate acceleration when only speed is changing. To calculate acceleration without a change in direction, you just divide the change in velocity (represented by ) by the change in time (represented by ). The formula for acceleration in this case is:. Answer: time
[A]:
To calculate acceleration without a change in direction, you just divide the change in velocity by the change in what?