A 2-year-old child known to suffer from recurrent bacterial infections and poor wound healing was found to have leukocyte adhesion molecule deficiency 1 (LAD-1). The leukocytes of this patient do not express CD18, a molecule classified as belonging to the family of:
a. selectins
b. integrins
c. lectin type of vascular adhesion molecules
d. aminotransferases
e. glycosidases

b. Integrins

Explanation:

Integrins are a family of plasma membrane proteins. These proteins are involved in the process of signaling between the cell interior and the extracellular matrix. Integrins are heterodimeric proteins and have two different subunits called alpha and beta which are anchored to the plasma membrane by a transmembrane helix.

Integrins have binding sites for many extracellular macromolecules as they also serve as receptors and signal transducers. Integrin gene codes for the beta subunit of adhesion molecule of leucocytes which is also called CD18. Mutation in this integrin gene results in leukocyte adhesion deficiency in humans.  

life would be meaningless without memes

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)