Jen has fair skin, and both her mother and her aunt have been treated for skin cancer. This coming weekend, Jen and her friends are planning an all-day outdoor hike near a high-elevation mountain lake; she expects there will be a mix of sun and shade on the trail and at the lakeshore beach. She is looking forward to the hike, but she wants to avoid getting a sunburn or any sun damage. Jen applies sunscreen to the exposed areas of her skin before she leaves her apartment for the hike; she should apply more sunscreenA. after climbing a hill and sweating heavily. B. 30 minutes before sun exposure begins. C. 2 hours after sun exposure begins. D. All answer choices are correct.