Hormones are signaling substances that bind
a. to clefts in the cell wall.
b. to receptor proteins
c. at nerve endings.
d. through capillaries.
e. in the lymph system.

b. to receptor proteins

Explanation:

Hormones can be defined as chemical  messengers which enhances communication between the body cells and carry out specific regulating functions.

Hormones are secreted in the endocrine gland and  they can be classified based on their chemical nature, mechanism of action, nature of action and  their stimulation in the endocrine gland.

hormone activates target  cells in such a way that it diffuses through the  target cell plasma membrane to bind to a  receptor protein in the cytoplasm of the cell

69 is the correct math for the amino acids