Question

Fill in the blank with a suitable preposition
Switch ________ a light. It’s getting dark.
a) Of
b) off
c) out
d) on

Answer 1

Hint: Prepositions are used before a word to show the relation with another word. The man put the decorations in the box. It tells the position of the decorations- in the box. It is not on the box or beside the box. It is telling us the relation of the word with another word.

Complete answer:
Option a is wrong because “of” means to show constituents of something. For example, she was wearing a dress made of silk. What was the dress made of? Silk. So the word “of” is telling us the constituent of the dress- silk.
Option b is the wrong answer because “off” has a lot of meanings- to be at a distance, to remove something, etc. So we generally use “off” with turning a switch off. We switch off a light when there is too much light. But since the question is talking about the fact that it’s getting dark, they need light. So they obviously don’t want to switch off the light.
Option c is wrong. An example of a sentence with “out” is: The lights went out. This means the lights turned off.
Option d is correct because you turn/switch on a light to be able to see things in the dark. Thus, because it is getting dark (as given in the question), the switch of the light to see in the dark.

Note:
These are some common phrases that always go together: turn on the switch, turn off the switch, put on the light, etc. They are commonly termed phrasal verbs. No other preposition can be used in such sentences. Therefore, these need to be learned.