单选题 Liver disease is the 12th -leading cause of death in the U. S. , chiefly because once it's determined that a patient needs a new liver it's very difficult to get one. Even in case where a suitable donor match is found, there's no guarantee a transplant will be successful. But researchers at Massachusetts General Hospital have taken a huge step toward building functioning livers in the lab, successfully transplanting culture-grown livers into rats. The livers aren't grown from scratch, but rather within the infrastructure of a donor liver. The liver cells in the donor organ are washed out with a detergent that gently strips away the liver cells, leaving behind a biological scaffold of proteins and extracellular architecture that is very hard to duplicate synthetically. With all of that complicated infrastructure already in place, the researchers then seeded the scaffold (支架) with liver cells isolated from healthy livers, as well as some special endothelial cells to line the bold vessels. Once repopulated with healthy cells, these livers lived in culture for 10 days. The team also transplanted some two-day-old recellularized livers back into rats, where they continued to thrive for eight hours while connected into the rats' vascular systems. However, the current method isn't perfect and cannot seem to repopulate the blood vessels quite densely enough and the transplanted livers can't keep functioning for more than about 24 hours (hence the eight-hour maximum for the rat transplant). But the initial successes are promising, and the team thinks they can overcome the blood vessel problem and get fully functioning livers into rats within two years. It still might be a decade before the tech hits the clinic, but if nothing goes horribly wrong — and especially if stem-cell research establishes a reliable way to create healthy liver cells from the very patients who need transplants — lab-generated livers that are perfect matches for their recipients could become a reality.

单选题 It can be inferred from the passage that the animal model was mainly intended to______.

【正确答案】 D

【答案解析】解析：推理题。题干：从文中可推理得知，动物模型主要目的是______。从文中首段可知，目前美国第十二大致命杀手便是肝脏疾病，主要是因为一旦患上这种疾病，患者需要移植一颗新的肝脏，但是要找到完全匹配的肝脏非常困难。因此动物模型主要是为了解决肝脏来源的问题。故本题答案为D。

单选题 What does the author mean when he says that the livers aren't grown from scratch?

单选题 The biological scaffold was not put into the culture in the lab until______.

【正确答案】 C

【答案解析】解析：细节题。题干：生物支架在______才会放进实验室的培养液中。用culture回到原文定位到第三段，可知当这些复杂的基础框架准备好后，研究者将从健康肝脏里分离出来的肝脏细胞和粗血管上的内皮细胞植入蛋白质支架之中。健康的肝脏细胞植入之后，肝脏便能够在培养基中存活10天。因此正确答案应该是“植入健康的肝脏细胞”。故本题答案为C。