Fill in the blank with a suitable preposition.
His ambition was _______ become a fighter pilot and serve his nation.
The preposition ‘to’ is used to refer to advancing towards a particular thing. In the sentence, the person wants to become a fighter pilot which is his motive. In addition to this, the preposition ‘to’ is commonly used to connect one verb to the other. The two verbs here are 'was' and 'become'. Hence option B is correct. On the other hand ‘for’, ‘of’ and ‘by’ are unsuitable. ‘For’ is used to indicate a reason, ‘of’ denotes belonging while ‘by’ refers to an agent who performs the action. The blank is followed by none of these three. In addition to that 'for', 'of' and 'by' cannot be used to connect two verbs, hence options A, C and D are incorrect.