In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.

Question: What begins approximately six weeks after fertilization in an embryo? Answer: ossification
Ossification begins approximately six weeks after fertilization in an embryo.

Question: How do prokaryotic organisms reproduce asexually? Answer: binary fission
Prokaryotic organisms reproduce asexually through binary fission.

Question: What are substances that cannot be broken down into simpler substances with different properties called? Answer: elements

Substances that cannot be broken down into simpler substances with different properties are called elements.