Answer:
(b) 7 characters: 4 Numbers, 1 Lowercase Letter, 1 Uppercase letter, 1 Symbol
Explanation:
The best rule that makes a password great is that rule that increases the entropy of the password. The entropy of a password is the measure of how easy it is for the password to be cracked e.g by guessing, by brute force cracking, by dictionary attacks and other related cracking methods.
A rule that makes use of a logical combination of the four types of characters - digits, lowercase letters, uppercase letters and special symbols - gives a greater strength to the password than the rules that just make use of the some of the four types of characters.
Increasing the length of the password too is a great way of increasing the entropy of the password. But then, if there is a trade-off between length and combination, the latter is better.
