Jeff is 13 years old and has recently noticed some remarkable changes in himself.Over the past few months his voice has started to change,growing deeper.He has begun to grow pubic hair,as well as the beginnings of a facial beard.He is also filling out,with his muscles developing rapidly.These changes in Jeff are probably due to the action of the

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The changes Jeff is experiencing, such as the deepening voice, growth of pubic hair and facial hair, and rapid muscle development, are all typical of puberty and are primarily due to the action of the gonads (testes in males, ovaries in females).

Jeff Is 13 Years Old and Has Recently Noticed Some