Final answer:
The statement by the client that indicates the need for further teaching is D) 'I'll be sure to use a sunscreen with at least SPF 30 during the day.'
Step-by-step explanation:
The statement by the client that indicates the need for further teaching is D) 'I'll be sure to use a sunscreen with at least SPF 30 during the day.' The need for further teaching is indicated because tretinoin increases the skin's sensitivity to the sun, making it more susceptible to sunburn. The client should be advised to completely avoid sun exposure while using tretinoin, as even with sunscreen, the risk of skin damage and sunburn is increased.