What is the role of a control group in any experiment

Which sequence represents a cross section of the bilayera hydrophilic head, hydrophobic tail, hydrophobic tail, hydrophilic headb hydrophobic tail, hydrophilic head, hydrophobic tail, hydrophilic headc hydrophobic head, hydrophilic tail. hydrophilic tail, hydrophobic headd hydrophilic tail, hydrophobic head, hydrophobic head, hydrophilic tail

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

This is one form of rna that transports a specific amino acid to a ribosome during protein synthesis.