Fill in the blank with a suitable preposition:
Sauté the vegetable ________ it is soft enough to eat.
(a)Within
(b)Until
(c)By
(d)To

Hint: Read the given sentence carefully. Try to make out the core meaning of it. Find out the subject, predicate and the object of the given sentence.

Complete answer: In the given options, the preposition ‘within’ is used to denote that an action is set to happen anytime inside a particular period of time. For example : "within an hour" or "within five minutes". The sentence here doesn’t speak about a fixed time period, instead refers to a point till which something is to be done. In addition to this, ‘within’ when used as a preposition has to be followed by a noun, since ‘it’ is not a noun, option ‘a' is incorrect.
Similarly, the prepositions ‘by’ and ‘to’ are used to denote an endpoint should be followed by a unit of time or a noun to be grammatically appropriate. Thus, options ‘c’ and ‘d' are incorrect. On the other hand, the preposition ‘until’ is used to refer to the time till which an action takes place. In the given context the vegetables need to be sautéed till they are soft and completely cooked.
As we have analysed all the given options to find out the correct option. Here, the correct word to be filled in is – until. The complete sentence would be – Sauté the vegetable until it is soft enough to eat. Hence, option ‘b’ is the correct option.

Note:All the other options are plausible distractions. Don’t confuse between ‘by’ and ‘until’. They both have different meanings and different usage.