Answer:
D in pairs
Explanation:
Forces always come in pairs - equal and opposite action-reaction force pairs.
Answer:
Transformer
Explanation:
Transformers can increase (step up), or it can decrease (step down) voltage.
The Doppler effect is when the frequency of a sound changes as the position of you and the sound changes. For example, if a fire truck comes at you, the siren sound will increase, then, after it passes you, then the sound will decrease. The thing that just happened is the Doppler effect!
Have a nice day! :)