What is a star's main fuel during its lifetime? a. hydrogen b. carbon c. helium d. oxygen

Fill in the blank. the number of each type of element in the compound (other than 1) is represented by a small number to the right of the element symbol.

In a simplified model of the human eye, the aqueous and vitreous humors and the lens all have a refractive index of 1.40, and all the refraction occurs at the cornea, whose vertex is 2.60 cm from the retina. what should be the radius of curvature of the cornea such that the image of an object 40.0 cm from the cornea’s vertex is focused on the retina?

When using the scientist method, which step comes last?