Answer the following question given this paragraph: 

Puberty in girls starts when the hypothalamus “tells” the pituitary gland to secrete hormones that target the ovaries. Two pituitary hormones are involved: luteinizing hormone (LH) and follicle-stimulating hormone (FSH) . These hormones stimulate the ovary to produce estrogen . Estrogen, in turn, promotes growth and other physical changes of puberty. It stimulates growth and development of the internal reproductive organs, breasts, and pubic hair (see Figure below ). You can watch an animation of these and other changes that girls experience during puberty at this link: http://www. bbc. co. uk/science/humanbody/body/interactives/lifecycle/teenagers/ .


Q: What item starts puberty in girls?

 Choices:

- the ovary

- the uterus

- the thyroid

- the hypothalamus

A:
the hypothalamus
