Oxygenated blood returns to the left atrium through which of the following?

A. Luteinizing hormone (LH) is involved in the regulation of the menstrual cycle and ovulation, but it is not responsible for uterine contractions or milk production.
B. Lactogen (also known as human placental lactogen) is produced during pregnancy and helps prepare the breasts for milk production, but it does not trigger uterine contractions.
C. Oxytocin plays a key role in both uterine contractions during labor and milk ejection during breastfeeding. It is sometimes referred to as the "love hormone" because it is also involved in bonding and emotional connections.
D. Prolactin is responsible for stimulating milk production in the mammary glands, but it does not cause uterine contractions. Oxytocin is the hormone responsible for that function.

A. Generating and transmitting impulses is the primary function of nervous tissue, not connective tissue. Nervous tissue is responsible for carrying signals throughout the body.

B. Covering and lining body surfaces is the function of epithelial tissue, which forms the skin and the lining of organs, not connective tissue.

C. Contracting and bringing about movement is the function of muscle tissue, not connective tissue. Muscle tissue is responsible for contraction and body movement.

D. Connective tissue's main function is to bind other tissues together and provide structural support. It includes tissues such as bone, blood, cartilage, and tendons, all of which help support, protect, and connect other tissues and organs.