The first line of defense involves which structures a. t-cells b- skin c. blood d. b- cells

  B. Skin

Explanation:

  The human body has a two-line defense system. The first line is known as outside protection and includes physical and chemical barriers that are always ready to defend the body.

  The skin is the largest organ of the body and it´s a barrier between the organs and the outside.

  I hope this answer helps you.

the atm that sounds like it should be the answer

they encountered severe weather for which they were poorly prepared.