Statement: “Never use obvious PINs like your car registration number, birth date, or telephone number. Change your PIN every three months.” — Instruction to bank customers with ATM facilities.\nAssumptions I & II:\nI. ATM cards issued by a bank to customers might be lost or stolen by some customers.\nII. Some people may try to use others’ ATM cards clandestinely to withdraw money.\nChoose the option that correctly identifies the implicit assumption(s).

Introduction / Context:
The guidance warns against obvious PIN choices and recommends periodic changes. Such advice is a classic defense against unauthorized access. We must determine the minimally necessary assumptions enabling the advice to have purpose.

Given Data / Assumptions:

• I. Cards can be lost/stolen or otherwise fall into unauthorized hands.
• II. There exist actors who might attempt to use someone else’s card (with or without the correct PIN) to withdraw funds.

Concept / Approach:
For PIN hygiene advice to matter, two risks must be plausible: (a) card possession by an unauthorized party and (b) attempts to guess or acquire the PIN. If either were impossible, the advice would be pointless. Obvious PINs (birth dates, etc.) aid guessing—especially when the attacker knows the victim.

Step-by-Step Solution:
1) “Never use obvious PINs” presumes adversaries may try to infer PINs from known personal data, which is relevant only if attackers could get the card (I) and try to use it (II).2) “Change your PIN every three months” mitigates risks from shoulder-surfing, leaks, or temporary access, again presupposing the possibility of misuse (II) and occasional loss/theft or duplication of cards (I).3) Thus both I and II underpin the recommendation.

Verification / Alternative check:
If cards could never be lost/stolen, or if nobody would attempt misuse, periodic PIN changes and avoiding obvious PINs would be unnecessary.

Why Other Options Are Wrong:
Only I/Only II/Either: each omits one necessary flank of the risk model. Neither: contradicts the very rationale for security advice.

Common Pitfalls:
Assuming online-only risk; ATM misuse is primarily possession + PIN guessing. Obvious PINs catastrophically lower guessing cost.

Final Answer:
Both I and II are implicit.