At the age of 13 is it normal to have menstruation 2 times a month or you should be worried.

It's often normal during the teen years to have irregular periods. When a girl's period is irregular, it might come more than once a month or only come every few months. Some girls find they get their period more than once some months, then they might not have another for several months.

Explanation:

the answer is z.

the human body has five levels of organization. level 1: cells. cells are the basic units of life and form the first level of organization. cells in the human body have specific functions. examples include nerve cells, blood cells, liver cells, and so on.