What part of an experiment is used to show that results are due to the condition being tested

The majority of sulfur dioxide produced by industry comes from a. oil refineries. b. dry cleaners. c. chemical plants. d. coal-burning power plants.

Where do homologous chromosomes exchange genetic material through crossing over?               a.  chlorophyll    b.  centrosomes    c.  centromeres    d.  chiasma

The response is the basis for vaccination. primary secondary tertiary none of the above