Instruction — “Do not hold the cellphone or keep it in your pocket if you are very close to fuel fumes.”\nQuestion — Which conclusion necessarily follows from this safety instruction?

Introduction / Context:
A safety instruction warns against keeping/using a cellphone near fuel fumes. We must infer what the instruction presupposes or implies, without adding unrelated technical claims about device materials.

Given Data / Assumptions:

• The instruction links proximity to fuel fumes with a prohibition on holding/carrying a cellphone.
• It is framed to prevent risk.

Concept / Approach:
Safety warnings generally imply a non-zero risk that the warned-against action could cause harm under those conditions. Here, it implies a possibility that a cellphone might ignite vapours (e.g., via spark, battery, electronics), hence the caution.

Step-by-Step Solution:

Verification / Alternative check:
Even if a phone’s casing is not highly inflammable, ignition risk can remain due to electrical behaviour around flammable vapours. Thus I follows while II does not.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing “can ignite vapours” with “is itself highly inflammable.”

Final Answer:
if only conclusion I follows