How many colors are there in a rainbow? Seven! There are seven __9__ (continent). Some researchers have found that human memory works best when __10__ (remember) up to - but not more that - seven items.

　　Mathematically, the number seven is an odd number. Even numbers can be easily divided by two, so odd numbers seem more unique to some people.

　　答案：1.asked　2.a　3.In　4.is considered　5.itself

　　6．Whether　7.simply　8.will find　9.continents

　　10．remembering