Question

two kinds of radiation make up the light from the sun that penetrates the atmosphere and reaches earth: long wave ultraviolet a (uva) and short wave ultraviolet b (uvb). though uvb rays tend to damage the skins outer layers, causing redness and sunburn, uva rays penetrate the skins thickest layer, known as the dermis. it was once thought that only uvb rays were cause for concern. over the years, however, scientists have learned more about how uva rays damage skin cells in the basal layer, where a majority of skin cancers form. now we know that uva rays pose dangers similar to those from uvb rays in terms of skin cancer development. in addition, both types of rays contribute to the premature aging of skin.

Explanation:

• The text states that "Two kinds of radiation make up the light from the sun that penetrates the atmosphere and reaches Earth: long wave ultraviolet A (UVA) and short wave ultraviolet B (UVB)". So both UVA and UVB penetrate the atmosphere.
• It also says "UVA rays penetrate the skin's thickest layer, known as the dermis". So only UVA penetrates the dermis.
• Regarding skin cancers, "Now we know that UVA rays pose dangers similar to those from UVB rays in terms of skin cancer development". So both play a role.
• For skin aging, "both types of rays contribute to the premature aging of skin". So both play a role.

Answer:

• Penetrate the atmosphere: UVA rays (✔), UVB rays (✔)
• Penetrate the dermis: UVA rays (✔), UVB rays (✖)
• Play a role in skin cancers: UVA rays (✔), UVB rays (✔)
• Play a role in skin aging: UVA rays (✔), UVB rays (✔)