1 . The ________ (absorb) of vitamin D is essential for maintaining strong and healthy bones. (所给词的适当形式填空)

2 . Noise control materials can be tested in terms of sound ________(absorb). (所给词的适当形式填空)

3 . Both scattering and_____(absorb) of light make an object look different from other objects around it, so you can see it easily. (所给词的适当形式填空)

4 . 他意识到过多的咖啡因摄入产生了刺激效果，并妨碍了他的睡眠。(aware) (汉译英)