A doctor and a bus driver are both in love with the same woman, an attractive girl named Sarah. The bus driver had to go on a long bus trip that would last a week. Before he left, he gave Sarah seven apples. Why?

“The bus driver wanted to impress Sarah with gifts.”

While giving apples could be seen as a gesture to impress, it doesn't relate to the riddle's underlying theme of keeping the doctor away.

“The apples were for Sarah's health.”

Though apples are healthy, the riddle specifically ties the number of apples to the phrase 'an apple a day keeps the doctor away,' emphasizing the reason behind the apples rather than general health.

“The bus driver wanted Sarah to remember him while he was gone.”

This guess reflects a sentimental motive, but it misses the clever play on words and the pun involving the doctor and the apples.