Nobody likes doing the dishes, but it turns out that doing this daily task might pay off in an unexpected way. According to a new study published in the Journal of Pediatrics, washing dishes by hand instead of using a dishwasher might prevent the development of allergies.

    Researchers in Sweden surveyed the parents of 1,029 children ages 7 and 8. They discovered that children whose families hand-washed the dishes instead of using a machine were less likely to have allergies.

    Earlier research has shown that dishes washed by machine are cleaner than those washed by hand. So why would kids who eat off slightly dirtier plates be better off when we talk about preventing allergies? One explanation is based on a theory known as the "hygiene hypothesis (卫生假说)," which says the reason why kids develop allergies is that their surroundings are actually too clean.

    Your immune (免疫) system keeps you healthy by fighting germs (病菌) like bacteria and viruses. But when you have allergies, it overreacts and tries to fight ordinary things like pollen (花粉) or certain foods.

    Being exposed to germs, particularly early in life, is good training for the immune system, says the lead author of the study, Dr. Bill Hesselmar of Queen Silvia Hospital in Sweden. "You excite the immune system in various ways and it becomes tolerant."

    This study shows that while using the dishwasher might be easier, the old-fashioned method of cleaning up could be better for your health.

继“天宫”一号空间站之后，我国又发射“神舟八号”无人飞船，它们的运动轨迹如图所示。假设“天宫”一号绕地球做圆周运动的轨道半径为r，周期为T，万有引力常量为G。则下列说法正确的是（   ）

Would you please tell me________to deal with all the problems, Mr Feng?

设函数f（x）在x₀处可导，则$\underset{△x\to 0}{lim}\frac{f\left(x_0-△x\right)-f\left(x_0\right)}{△x}$等于（　　）

20世纪初，站在宣传马克思主义前列的是(     )