Which sentence must be revised to eliminate the preposition at the end?

If no one answers the door, then please let yourself in.
The top steps are fine, but be careful of the slippery stairs below.
Where are Katelyn and Ella walking to?
Do you know what Naveen was talking about?

Choose one of the topics below and use all five sentence patterns in a composition of at least 100 words. return to the lessons "patterns: inverted, compound parts, s/v/do" and "patterns: s/lv/pn, s/lv/pa, s/v/io/do" if you need to review the sentence patterns. you will be graded based on whether all five sentence patterns are present in your work. suggestions for topics: a. what if the sun exploded? b. what if every family owned a helicopter? c. what if each year were six months long instead of twelve? d. what if you were the president of the united states?