The parents have devoted themselves to bringing up their children and now it is time for the children, ______, to show their devotion to their parents.

A．in their turn

B．in their return

C．in return

D．in their turns

汽车上的散热器用水作为冷却剂，这是利用了水的 __________ 较大的性质；散热器中装有10kg的水，在温度升高20℃的过程中，水吸收的热量是 __________ J，这些热量相当于完全燃烧 __________ kg的天然气放出的热量【水的比热容c_水=4.2×10³J/（kg·℃），天然气的热值q=8.4×10⁷J/kg】.