Explanation:

Computers can be broadly classified based on their working style or how they process data. The two primary categories are (a) Digital computers, which process discrete data (represented as binary digits, $0$s and $1$s), and (b) Analog computers, which process continuous data (represented by continuously varying physical quantities like voltage or pressure). Options (c) Micro and (d) Mini refer to classifications based on size, cost, and processing capacity, not their fundamental working style. Therefore, both Digital and Analog are types of computers based on their working style, making 'a and b both' ($ \text{e} $) the correct answer.