She must attend . . . . . . . . the lecture. A. to B. in C. on D. with

The correct answer is A. to.

The preposition “to” is used to indicate a destination or goal. In this case, the lecture is the destination that the woman must attend.

The other options are incorrect because they do not indicate a destination or goal.

• The preposition “in” is used to indicate a location or position. In this case, the lecture is not a location or position, but an event.
• The preposition “on” is used to indicate a surface or area. In this case, the lecture is not a surface or area, but an event.
• The preposition “with” is used to indicate association or accompaniment. In this case, the woman is not associated with the lecture, but is attending it.