Geo-informatics is a multidisciplinary field that combines various techniques and technologies to collect, analyze, and interpret geospatial data for solving complex problems related to geography and the environment. The correct answer, option 'A', includes three key techniques that are commonly used in geo-informatics: remote sensing, GIS (Geographic Information System), and GPS (Global Positioning System).

1. Remote Sensing:
Remote sensing involves the acquisition of information about an object or phenomenon without being in direct physical contact with it. It uses devices such as satellites, aircraft, or drones to gather data from a distance. This technique allows us to collect data about the Earth's surface, atmosphere, and oceans. Remote sensing data can be in the form of images, which provide valuable information about land use, vegetation cover, urban development, etc.

2. GIS (Geographic Information System):
GIS is a computer-based system used to capture, store, analyze, and display geospatial data. It allows the integration of various types of data, such as maps, satellite imagery, and survey data, into a single database. GIS enables spatial analysis and modeling, making it a powerful tool for decision-making and problem-solving in fields like urban planning, environmental management, and disaster response. It provides the ability to overlay different layers of information and extract meaningful insights.

3. GPS (Global Positioning System):
GPS is a satellite-based navigation system that allows users to determine their precise location on the Earth's surface. It works by triangulating signals from multiple satellites to calculate the receiver's position. GPS technology is widely used for navigation, surveying, and mapping purposes. It provides accurate and real-time positioning information, which is essential for various applications like vehicle tracking, wildlife conservation, and emergency response.

These three techniques, remote sensing, GIS, and GPS, are the fundamental pillars of geo-informatics. They complement each other and are often used together to collect, analyze, and interpret geospatial data. By combining these techniques, researchers and professionals can gain valuable insights into the Earth's physical and human systems, leading to better decision-making and sustainable development.