Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions

      Hay fever is a common allergic condition that affects up to one in five people at some point in their life. Symptoms of hay fever include watery and itchy eyes and a runny, congested nose. People suffering from hay fever may experience occasional wheezing and repeated bouts of sneezing and may even lose their sense of smell. Some may also have stopped-up ears. About 30 percent of those who suffer from hay fever may develop the symptoms associated with periodic asthma or a sinus infection. The allergen-antibody theory does not fully explain allergic reactions because the membranes and glands in eyes and ears are controlled by the independent nervous system, which keeps these organs in balance. But the independent nervous system itself is part of the emotional- response center and may cause the feelings of anger, and lack of self-confidence in reaction to allergy-causing substances. 

      The most common cause of hay fever is the pollen of ragweed, which blossoms during the summer and autumn. When airborne pollen particles, as well as mould, come into contact with the victim's membranes, they can cause allergic reactions that release histamine and result in virtual blockage of air passages. To prevent hay fever or to decrease the severity of its symptoms, contact with the ragweed pollen should be reduced. If possible, stay indoors when the pollen count is high (over 50). Remember to keep windows and doors shut in your house. If it gets too warm, draw the curtains to keep out the sun and lower the temperature. If possible, avoid drying clothes outside. This will help to stop pollen being brought into your house. If you need to go outside or you're travelling, avoid cutting grass, playing or walking in grassy areas and camping - particularly in the early morning; evening and at night, when the pollen count is at its highest. Don't forget to wear wraparound sunglasses to stop pollen getting in your eyes as well. 

      Although some communities have attempted to eliminate the plants that cause the reactions, elimination programs have not been successful because airborne pollen can travel considerable distances. Antihistamine can help with short but severe attacks. Over extended periods of time, however, patients are prescribed a series of injections of the substance to which they are sensitive in order to increase immunity and thus be relieved of the seasonal allergy. 

The word “blockage" in the passage is closest in meaning to ________.

• A. 
  dryness
• B. 
  bleeding
• C. 
  obstruction
• D. 
  enlargement