Can... Could

Question 1

can or could

Answer 1

“Could” is the polite form of “can”—so both are correct, but we use them in different situations. We use “can” when we are telling someone to do something. We use “could” when we are making a request.

Teacher to students: “Can you please be quiet!”
Student to teacher: “Could you please explain it once again?”

Question 2

turn on or switch on

Answer 2

1 : to turn off (something) by turning or pushing a button or moving a switch, lever, etc. He switched off the light/lamp. He switched the TV off. 2 informal : to stop paying attention When the topic turned to the stock market, he switched off.

Question 3

switch on or turn on

Answer 3

Any electric appliance that has an on-off switch (or on/off button) can be “switched on/off”. Eg. Switch on the lights/television etc. You can “turn on” any electric appliance, even if it does not have an on-off switch.