Select the most appropriate meaning of the idiom.

Back in saddle

Resume duty

The answer is Resume duty.

The idiom "back in the saddle" means to return to something that you have been doing before. It is often used to describe someone who is returning to work after a break, or to someone who is returning to a sport or activity that they have not done in a while.

In the sentence, the person is "back in the saddle" because they are resuming their duties as a doctor. They have been away from work for a while, but they are now back and ready to start working again.

The other options are not correct. Learning how to ride is not the same as returning to something that you have been doing before. Teaching someone riding is not the same as resuming your own riding. And putting a new saddle is not the same as returning to riding.