In many species of animals, at the onset of pregnancy, $\mathrm{LH}$ is released; it promotes the synthesis of progesterone- a major hormone in maintaining the pregnancy.
(a) Where is LH produced, and to what class of hormones does it belong?
(b) Where is progesterone produced, and to what class of hormones does it belong?
(c) Do progesterone-producing cells have LH receptors on their surface, or does $\mathrm{LH}$ enter the cell to carry out its function?
(d) Does progesterone bind to a cell-surface receptor, or does it enter the cell to carry out its function? Explain.