7. how do scientists use electromagnetic emissions of stars to determine their composition, age, and stage of development?

The Fraunhofer lines of stars are caused by the emitting of light or of absorbing it at particular wavelength from a particular element which determines the composition, age and development stage of stars.

Explanation:

Through the study of electromagnetic emission of stars it is now possible for scientists to know about the composition, development and age of a star. As the Fraunhofer line exhibited from stars are caused by the elements that emits and absorbs light at a particular wavelength, the composition of the star can be determined by it.

Through the composition, the star age is known to the scientists now. By studying the spectra wavelengths one can know the temperature of it and this temperature determines their age.  

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

hey, i believe your answer would be d. sugar ribose and the base uracil. i believe this is the answer, because rna consists of sugar ribose, adenine, guanine, cytosine, and uracil.

your first option is incorrect, because that's dna. where it consists of sugar deoxyribose, adenine, guanine, cytosine and thymine.

your second option is also incorrect, this is because sugar deoxyribose is in dna, and uracil is in rna. these two do not make sense together.

your third option being incorrect, because sugar ribose is in rna, but not the base of thymine. rna consists of uracil, not thymine.

lastly your fourth option being correct! this answer is correct, because both sugar ribose, and the base uracil are in rna! ~

answer is d. sugar ribose and the base uracil.