For questions 17-21, write the letter of the definition that best matches the term or phrase in the space provided : 17. Quasar
18. Cosmic background radiation
19. Nova
20. Protostar
21. Pulsar
A. A shrinking region of space flattened into a disk with a central concentration of matter.
B. An object that produces energy at a high rate at the center of some galaxies.
C. A neutron star that emits radio waves.
D. Possible evidence of the big bang.
E. A large, bright explosion of a white dwarf caused by pressure building up

(Which Letter should go on what box up top? Please help! <3)

answer: if she breaths she a thho

explanation:

1. amino acid refers to the fundamental building block of proteins, comprising of an amino group and a carboxyl group.

2. catalyst refers to any substance, which increases the rate of chemical reaction without being used up in the reaction.

3. a complex molecule containing he genetic code is dna or deoxyribonucleic acid.

4. an enzyme refers to a molecule of protein, which is unique in accelerating up a particular chemical reaction in the biological systems.

5. nucleic acid refers to an sequence of sugars, phosphates, and nitrogenous bases, for example, dna and rna.

6. a protein refers to a large, composite organic molecule comprising of a huge number of amino acids associated together with the of peptide bonds.

7. rna refers to a nucleic acid that takes part in the production of proteins.

8. substrate refers to a compound, which takes part in a chemical reaction, and is chemically modified by the reaction.