根据提示补全下列教材原句

　　1．An Italian doctor wants to offer cloning as an optional treatment for couples who children.

　　一位意大利医生想把克隆作为不孕夫妇的一种选择性治疗方案。

　　2． some voluntary code of practice among scientists has to be agreed.

　　很明显，科学家们的一些非官方的行医法规必须被获准。

　　3． by Hammond's two grandchildren, they are sent on a tour through Jurassic Park in computer­controlled cars.

　　在哈蒙德的两个孙子的陪伴下，他们被送到电脑控制的轿车中进行环绕侏罗纪公园的旅行。

　　4．But a tropical storm hits the island, the power supply，and an employee destroys the security system so that he can steal dinosaur embryos and sell them.

　　但是一场热带风暴袭击了该岛屿，摧毁了电力供应，一个雇员破坏了安全系统，因此他能偷出恐龙胚胎并卖掉它们。

　　5． Brave New World is still so famous it describes a terrifying future world that is becoming more and more possible.

　　《勇敢新世界》这本书现在仍然很出名，原因是它向我们展现了一个可怕的未来世界，并且这个世界越来越可能成为现实。

　　【答案】　1.find it difficult to have　2.What is clear is that　3.Accompanied　4.knocking out　5.The reason why；is that

　阅读P64～65教材原文，从四个选项中选择最佳答案

　　Stem cells can be used to ．

A．develop into enzymes