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: When does exchange of dna segments happen between non-sister chromatids of homologous chromosomes? Answer: during crossing-over
Exchange of dna segments happens between non-sister chromatids of homologous chromosomes during crossing-over.

Question: What occurs when a population reaches the carrying capacity? Answer: growth stops
Growth stops when a population reaches the carrying capacity.

Question: What harmful substance must not be drained into s storm sewer? Answer: motor oil
Motor oil is a harmful substance that must not be drained into a storm sewer.