Fill in the blank with a suitable preposition.
The students were shouting _______ the teacher entered the class.
If we use ‘to’ in the sentence, it would mean that the students were shouting at the teacher when he/she entered the class, since ‘to’ is used to show the person or thing that receives something. This is not an appropriate answer hence option A is incorrect. Similarly, the teacher is neither a unit of time nor a place, hence prepositions ‘within’ nor ‘in’ are unsuitable. ‘Within’ and ‘in’ are both used to speak about being inside a place/space or to denote a period of time. Therefore options C and D are incorrect. On the other hand, ‘till’ is used to speak about an action that lasts for a particular time period. It signifies the end of an action. Thus ‘till’ is the appropriate option here since it denotes that the students were shouting until the teacher arrived. This also signifies that the shouting was over after the teacher’s arrival. Thus option B is correct.