Assumption I: People read printed matter on a cigarette packet.
This is implicit because the warning assumes that individuals will read the information provided on the packet.
Assumption II: People take careful note of a warning.
This is also implicit, as the effectiveness of the warning depends on the assumption that people pay attention to and understand the warning.
Assumption III: Non-smoking promotes health.
This is not explicitly implied by the statement. While non-smoking can promote health, the warning about smoking does not directly assume or state this; it simply warns against the dangers of smoking itself.
So, the correct option is (B): Only I and II are implicit.