To solve this question, the user needs to understand the concept of a middle tier and its relationship with the database.

The middle tier is an intermediate layer between the client and the database. It typically consists of application servers, web servers, or other software components that handle business logic and data processing.

Now, let's go through each option and explain why it is right or wrong:

A. Increase the number: This option is incorrect. The middle tier can help manage and optimize database connections, reducing the number of direct connections to the database. By serving as a mediator between the client and the database, the middle tier can consolidate requests and establish a smaller number of connections to the database.

B. Have no effect on the number: This option is incorrect. The middle tier can have an impact on the number of connections to the database, as explained in the previous option.

C. Decrease the number: This option is correct. As mentioned earlier, the middle tier can consolidate requests and establish a smaller number of connections to the database. By handling multiple client requests and managing database connections efficiently, it can reduce the overall number of connections to the database.

D. It depends on the type of client: This option is incorrect. The number of connections to the database is primarily influenced by the middle tier's role in managing and optimizing database connections, rather than the type of client.

E. It depends on the type of database: This option is incorrect. The number of connections to the database is primarily influenced by the middle tier's role in managing and optimizing database connections, rather than the type of database.

The Answer is: C