Match the following:
| 1. Physical barriers | A. Acid in the stomach, saliva, tears |
| 2. Physiological barriers | B. Skin and mucus coating in respiratory, , and urogenital tracts |
| 3. Cellular barriers | C. Polymorpho-nuclear leukocytes (PMNL), macrophages, natural killer cells |
| 4. Cytokine barriers | D. Interferons secreted by virus-infected cells |
1
1-B, 2-A, 3-C, 4-D
2
1-D, 2-B, 3-C, 4-A
3
1-C, 2-A, 3-D, 4-B
4
1-C, 2-B, 3-D, 4-A