Where is the density of the material greater, at point a or point b

Ahypothesis that has been tested again and again , with similar results each time may become a law , true or false

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

Which of the following is a common response to cell signaling?