王妍的奶奶家养了2只公鸡、4只母鸡，共生蛋28个问平均每只鸡生了几个蛋？

下列需要急行胆道减压的疾病是（）。

A.急性胆囊炎

B.胆囊结石

C.肝内胆管结石

D.急性梗阻性化脓性胆管炎

E.胆囊结石嵌顿

Mike had just finished his lunch and was about to take a break _____ an unexpected visitor came.

A．when

B．while

C．so

D．for

电气火灾常用哪些类型的灭火器？

Why can human beings outlast many faster four legged animals when running long distances Perhaps because early humans evolved as hunters on the hot African savannas. Humans developed the ability to release heat by sweating, but most mammals must pant, a function hard to regulate while running. Also, four-legged animals must adopt a pace that lets them breathe once in mid-stride; otherwise, the impact of the front legs hitting the ground will prevent deep inhalation. Humans can vary the number of breaths per stride, set a pace unsuited to the prey, and so eventually exhaust it.
The author’s explanation of why human beings have evolved as superior distance runners would be most weakened if it were shown that

A．early humans typically hunted animals that were less well adapted than humans for long-distance running.

B．early humans were only one of a number of species that hunted prey on the African savannas.

C．early humans hunted mainly in groups by sneaking up on prey and trapping it within a circle.

D．hunting was just as essential for later humans in colder climates as it was for early humans on the African savannas.

E．(E) human beings of today have retained the ability to run long distances but no longer hunt by chasing prey.