Which of the following types of instruments responds to and displays information?

The correct choice is secondary instruments. These instruments play a crucial role in measurement systems, as they are designed to respond to variations in physical phenomena and present that information in a readable format. Secondary instruments typically process the output from primary instruments, which directly measure physical quantities.

For instance, a primary instrument might measure voltage, while a secondary instrument could take that voltage measurement and convert it into a pressure reading on a gauge that is easier to interpret. This makes secondary instruments vital for interpreting and displaying measurements in a way that can be effectively utilized by operators and technicians.

This distinction is important because primary instruments primarily focus on the direct measurement of a physical variable, whereas secondary instruments focus on the representation and interpretation of that data.