The use of electronic instruments is becoming more extensive because they have the capability to respond to signals from remote places and a fast response and compatibility with digital computers. This makes option (c) - both (a) and (b) - the correct answer.

Let's break down the reasons why electronic instruments are becoming more widely used:

1. Capability to respond to signals from remote places:
Electronic instruments can be designed to receive and process signals from remote locations. This is particularly useful in applications where it is not feasible or safe for humans to be present. For example, in space exploration, electronic instruments can be used to gather data from distant planets and transmit it back to Earth. Similarly, in industrial automation, electronic instruments can be used to monitor and control processes in remote locations.

2. Fast response and compatibility with digital computers:
Electronic instruments can provide quick and accurate measurements and responses due to their ability to process signals at high speeds. They can also be easily integrated with digital computers, allowing for efficient data acquisition, analysis, and control. This compatibility with digital computers enables advanced functionalities such as data logging, signal processing, and real-time control, enhancing the overall performance and reliability of electronic instruments.

3. High sensitivity but less reliability:
Option (d) - "a high sensitivity but less reliability" - is incorrect because electronic instruments can actually provide both high sensitivity and reliability. Electronic instruments can be designed with high precision and sensitivity, allowing for accurate measurements even in small signals. Additionally, advancements in technology have improved the reliability of electronic components, making electronic instruments more dependable in various applications.

In conclusion, the use of electronic instruments is becoming more extensive due to their capability to respond to signals from remote places and their fast response and compatibility with digital computers. These features enable electronic instruments to perform tasks efficiently and accurately, making them essential tools in a wide range of fields such as telecommunications, medical diagnostics, environmental monitoring, and scientific research.

B