B-cells defend the body against invaders by invading the bone ...

[viki]

B-cells defend the body against invaders by
 
  invading the bone marrow.
  attacking cancer cells.
  producing antibodies against bacteria and viruses.
  making the circulatory system more efficient.

Question 2

In the body's immune system, the attack cells, called B cells, are manufactured in the
 
  bone marrow.
  thymus.
  red blood cells.
  white blood cells.

[patma1981]

Answer to Question 1

producing antibodies against bacteria and viruses.

Answer to Question 2

bone marrow.