Select the correct option:
$(1)$ Approximately $97\%$ of $O_2$ is transported by plasma / RBCs.
$(2)$ The primary site of gas exchange is alveoli / bronchioles.

• A
  $(1)$ Plasma,$(2)$ Alveoli
• B
  $(1)$ RBCs,$(2)$ Alveoli
• C
  $(1)$ Plasma,$(2)$ Bronchioles
• D
  $(1)$ RBCs,$(2)$ Bronchioles