Primary structure of protein are created by what bonds

peptide bonds

Explanation:

A protein's primary structure is defined solely by its amino acid sequence, and is constructed by peptide bonds between adjacent amino acid residues. Secondary structure results from hydrogen bonding along the polypeptide backbone, resulting in alpha-helices and beta-pleated sheets.

the correct answer is 2 and 4

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.