6. After more than four decades of research and development, a new type of jet engine is being tested that could eventually propel aircraft anywhere in the world within two hours or help boost cargoes into space at significantly lower costs than current methods permit. A tested that could eventually propel aircraft anywhere in the world within two or help B. tested that could eventually have the capability of propelling aircraft anywhere in the world within two hours or to help C. tested, eventually able to propel aircraft anywhere in the world within two hours, or helping D tested, and it eventually could propel aircraft anywhere in the world within two hours, or helping E. tested, and it could eventually have the capability to propel aircraft anywhere I the world within two hours or help
10.There is ample evidence, derived from the lore of traditional folk medicine, that naturally occurring antibiotics are usually able to be modified to make them a more effective drug. A) are usually able to be modified to make them a more effective drug B) are usually able to be modified to make them more effective drugs C) are usually able to be modified, which makes them more effective drug D) can usually be modified to make them a more effective drug E) can usually be modified to make them more effective drugs
一个问题,can什么时候可以代替be able to? 记得以前作过一道题, "can often" 不能 代替“be often able to" 前者表是“能经常”,后者表示“经常能”, 意义不一样。
以下是引用xiang_y在2003-11-12 5:42:00的发言: 6. After more than four decades of research and development, a new type of jet engine is being tested that could eventually propel aircraft anywhere in the world within two hours or help boost cargoes into space at significantly lower costs than current methods permit. A tested that could eventually propel aircraft anywhere in the world within two or help B. tested that could eventually have the capability of propelling aircraft anywhere in the world within two hours or to help C. tested, eventually able to propel aircraft anywhere in the world within two hours, or helping D tested, and it eventually could propel aircraft anywhere in the world within two hours, or helping E. tested, and it could eventually have the capability to propel aircraft anywhere I the world within two hours or help