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.

do your own work

you really need to do your own work and stop cheating

those sounds of the natural world are bioacoustics, and they're more than a false-color spectrogram of data from the musiamunat conservation area.