Explanation:

The fundamental unit of digital information is a bit, which can be either a $0$ or a $1$. When $8$ of these bits are grouped together, they form a byte. This grouping allows for $2^8 = 256$ unique combinations, enough to represent various characters, numbers, and symbols. Option (a) 'megabyte' ($\text{MB}$) is a unit equivalent to $1024 \times 1024$ bytes. Option (b) 'kilobyte' ($\text{KB}$) is equivalent to $1024$ bytes. Option (c) 'gigabyte' ($\text{GB}$) is equivalent to $1024 \times 1024 \times 1024$ bytes. Option (d) 'byte' is precisely defined as a sequence of $8$ bits (eight $0$s and $1$s). This is the correct answer. Option (e) 'none of these' is incorrect because option (d) accurately describes the term.