Collocations are conventional combinations of words that naturally go together. (i) In standard English, students 'take' an exam (teachers 'give' exams). (ii) 'Have a seat' is a standard polite collocation used to ask someone to sit. (iii) 'Ran into' is the correct phrasal verb collocation for a vehicle collision. (iv) 'Take responsibility' is the fixed expression for assuming accountability. (v) 'Improve' naturally collocates with grammar and skills, whereas 'tone up' is used for physical fitness.