The answer for this question is: Atoms
A nitrogen atoms can make 3 covalent bonds because it has three unpaired electrons
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The immune system responds to antigens by producing cells that directly attack the pathogen, or by producing special proteins called antibodies. Antibodies attach to an antigen and attract cells that will engulf and destroy the pathogen. The main cells of the immune system are lymphocytes known as B cells and T cells.
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B I have taken the quiz already 90%
Transverse waves can be produced on a rope by moving one end of the rope up and down.The movement causes motion in the particles that make up the rope and the rope itself becomes the medium. The particles move perpendicular to the propagation. The movement also causes crests(highest point of the wave) and troughs (lowest point of the wave) which move along the direction of propagation.
