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  3. Medicine comes in many forms. In its liquid form, medicine affects the body very quickly. But the effects of liquid medicine arc

Medicine comes in many forms. In its liquid form, medicine affects the body very quickly. But the effects of liquid medicine arc

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问题    Medicine comes in many forms. In its liquid form, medicine affects the body very quickly. But the effects of liquid medicine arch’ t usually long-lasting. This is why pills and capsules (胶囊) are also used.
   The pills and capsules being sold today arch’ t perfect, either. Pills dissolve in the stomach. The medicine in the pills is released when the pills dissolve. But often, the pills dissolve too quickly.
   Scientists have been trying to develop a pill that can release medicine slowly over a long period of time. They have applied their knowledge  of plants to produce the "osmotic (渗透的) pump pill".
   The cell walls of plants are made of cellulose (纤维素). Cellulose is a very porous substance. Their holes are big enough to allow water through the cell walls. As water enters a cell, pressure builds up in the cell. The pressure pumps other substances out of the cell. These substances leave the cell through the cellulose wall. This slow, steady process is called osmosis.
   The osmotic pump pill is coated with synthetic cellulose. Liquid medicine is contained in the pill. The holes in the cellulose coating of the pill are big enough to allow water in the pill. As water from the body enters the pill, pressure builds up in the pill. The medicine is then slowly pumped out of the pill.
The passage implies that cellulose is a very porous substance because it contains______.
选项 A、a substance that creates pressure
B、millions of tiny holes
C、a substance that dissolves it
D、liquid medicine
答案B
解析 从porous一词的词义可以看出答案。
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