Question

Choose the word or phrase that best completes the sentence.
___________ they had been waiting in line all night, I was sure they'd get tickets.

a)As though
b)Because of
c)Since
d)Until

Answer 1

Hint: Try framing one sentence with each of the options given, if in case you can not remember which word would fit in the blank.

Complete step-by-step answer:

 The blank has to be filled with a preposition. Pre+position means a word coming before a noun or a pronoun and establishing a relationship between the elements of a clause or words. One by one we will see the meaning of each option and check if it sits in the blank.
The blank will be filled by a proposition which refers to time durations. Option ‘a’, As though is primarily used to make comparisons, or when you are giving a possible explanation for something or saying that something appears to be the case when it is not, nothing of this sort is happening in the sentence hence it is the incorrect option.
‘Because of’ is used when something becomes a cause of some other action. E.g ‘He died because of cancer’; here cancer is the cause of death of a person, again with this explanation, this option is also incorrect.
Option c ‘since’ is correct as it is used to express a starting point of time and the duration until now.
The last option is wrong as the sentence doesn't indicate the use of expressing a reason, a cause, and until doesn't indicate a starting point of time.

Note: Most of the time, prepositions are very confusing, so always remember to go by the rules and not by instinct.