Select the most appropriate meaning of the given idiom.

To work like a dog

To work very hard

The most appropriate meaning of the idiom "to work like a dog" is to work very hard. It means to put in a lot of effort and toiling, often without complaint. The idiom is thought to have originated from the fact that dogs are often seen as working animals, and they are often seen working long hours in difficult conditions.

The other options are not as appropriate. To have many pieces of work means to have a lot of tasks to complete. A government report is a document that is produced by a government agency. Upset the balance means to cause a situation to become unstable.

So, the answer is ☀.