1.Lung cancer, like some other cancers, often doesn’t produce ________ until it is too late and has spread beyond the chest to the brain, liver or bones.

　　A) trails

　　B) therapies

　　C) symptoms

　　D) symbols

　　2.With the increasing unemployment rate, workers who are 50 to 60 years old are usually the first to be ________.

　　A) laid off

　　B) laid aside

　　C) laid out

　　D) laid up

　　3.The physical differences between men and women can be ________ directly to our basic roles as hunters and child-bearers.

　　A) pursued

　　B) traced

　　C) switched

　　D) followed

　　4.It is clear that the dog has a much greater ________ of its brain devoted to smell than is the case with humans.

　　A) composition

　　B) compound

　　C) percent

　　D) proportion

　　5.American college students are increasingly ________ with credit card debt and the consequences can be rather serious.

　　A) boosted

　　B) burdened

　　C) discharged

　　D) dominated