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三、語文填空Passage 1Over the last few decades, researchers tinkering with molecules that turn an immune cell on andoff have created a revolutionary approach to fighting cancer. Instead of taking aim at the tumordirectly, this new class of medicines 21 the patient’s own immune cells to tackle the disease.Immune-based cancer therapies are saving thousands of lives, and the science behind them earnedthis year’s Nobel Prize in Physiology or Medicine. These drugs, called checkpoint blockers,appeared after scientists discovered molecules that help cancer cells block immune processes that22 a tumor otherwise. The secret lies with several “brake” proteins on white blood cells, T cells,that prevent the immune system 23 overreacting to microbial threats. Tumor cells have learned tosurvive by engaging the brake molecules, sending T cells into a stupor that allows cancer to gain afoothold. By thwarting this hijacking maneuver, checkpoint blockers release the brakes and awakenT cells to attack the tumor. A clever trick—24 that so far, these immune-based drugs only work inabout a fifth of cancer patients and for certain tumors, barely at all. To push past those limits, a fewcompanies are venturing into a new frontier—glycobiology, the science of the sugars that stud thesurface of cells. Sugars act like switches and knobs that control where and when a cell’s biologicalmachines, proteins and lipids, do their jobs. Yet for all their fine-tuning finesse and power, sugarsare highly complex molecules that have often 25 a deeper understanding of their workings becausethey are so hard to study in the lab.
21.
(A) harnesses
(B) harasses
(C) halts
(D) heaves

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