The answers that apply are; A, B, & C
Proteins work at a particular range of temperatures, working optimally at around 37 degrees (body temperatures). When the temperatures exceed 40 degrees, the protein becomes denatured. This means that it loses its structure because the high temperatures break the hydrogen bonds that play a significant role in its tertiary structure. When denatured, the protein is unable to perform its function because the active site is also lost or is no longer effective.