Final answer:
The most complex to least complex order is: Personal computer, PDA, server farm, supercomputer.
Step-by-step explanation:
The correct order of complexity for the given options is D. Personal computer, PDA, server farm, supercomputer.
A personal computer is the least complex device out of the given options, as it is designed for individual use and performs basic functions.
A PDA (Personal Digital Assistant) is more complex than a personal computer as it is specifically designed for mobile computing and includes features such as touchscreens and wireless connectivity.
A server farm is more complex than a PDA as it consists of multiple servers working together to handle and process a large amount of data and requests.
A supercomputer is the most complex device out of the given options, as it is designed to perform highly complex calculations and simulations at a much faster speed than regular computers.