Adelay in a young girls period means what?

This could be many things. It's common for young girls you have irregular periods but could also be a health problem. There is also a possibility of pregnancy if she is sexually active.

It can mean a lot of things really.

A delay in a period isn't unusual, it's quite common actually.

Some girls' periods arrive literally like clockwork while others might get theirs at slightly different times each month. But occasionally, a skipped period can happen during times of pressure or stress. It can also be because of the way you live. Maybe you decided to start working out more or you changed your diet. All of these things factor into a women or young girls period. 

Bmust be the answer, as technically all organs move, so a is incorrect. all organs are made of different types of cells, so that isn’t a problem, so c is also incorrect. human hearts are very similar to many other animals’ hearts, so d is also incorrect, yet the heart is made of muscle, which is hard to grow in the lab so it would be correct to say b