What is the hardest substance in the human body? can you answer this question and give me a source to where you got your answer from.

Fredrick griffith made a scientific discovery in 1928

Cells control gene expression at which steps

Earths energy sources include both renewable and nonrenewable resources. name at least three sources of energy that could be used in your house. then describe the ideal energy source for generating most of your homes electricity, and explain why you chose that source. can someone give me some ideas, i’m kinda confused.