题目

根据短文内容，从短文后的选项中选出能填入空白的最佳选项。选项中有两项为多余选项。 Different groups around the world areworking to expand the uses for mobile technology in health care. In the world, there are six billion mobilephone users in a population of seven billion people. Africa has widespread adoption.Three or four years ago the penetration(渗透) rates were20 percent or 30 percent, and now they're getting upwards of 60 percent in somecountries. Earlier research had been tolook at mobile technologies and AIDS. And so we have some great evidence o声音是由物体______产生的，月球上宇航员交谈用无线电这是因为______不能传声．