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The teacher paused as if ______ his students to ask questions on the point he had just said.

A. expecting B. to expect

C. having expected D. to have expected

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閱讀理解

Have you ever heard a news reporter talk about DNA?Reporters talk about DNA found at the scene of a crime.They talk about police finding DNA “fingerprints”.Police sometimes use DNA as a clue to find out who committed the crime.

DNA is a substance(物質)that makes up genes.Everything alive has genes.Plants have genes.Animals have genes.You have genes.

Genes are the basic units of heredity(遺傳).Heredity means all the characteristics you inherit from your parents.You get your genes from your parents.You inherit half of your genes from your mother.You inherit half of your genes from your father.

Genes are a kind of code.A tree’s genes tell what shape its leaves will be.A cat’s genes tell what color its fur will be.Your genes tell what color your eyes will be.Your genes tell what color your hair will be.Everything about you comes from the code in your genes.

Genes line up on strands(鏈)called chromosomes(染色體)in cells.Everything alive is made up of cells.Chromosomes are in the center,or nucleus of cells.

Different parts of you are made of different kinds of cells.Your muscles are made of muscle cells.Your skin is made of skin cells.The code in your genes tells your body to make different kinds of cells.The genes in each cell tell the cell how to work.They tell the cell when to make new copies of itself.

An Austrian monk named Gregor Mendel first saw inherited patterns in pea plants.He experimented with pea plants in the 1860s.One of the things,or traits(特質) Mendel studied was what makes some pea plants tall and some short.He said that the traits must come from units of heredity passed from the parent plants.These units were later called genes.

In the mid-1900s,scientists discovered that genes are made of DNA.In the 1970s,scientists learned how to change DNA with genetic engineering.Scientists also learned that problems with certain genes cause diseases.Muscular dystrophy,cystic fibrosis,and hemophilia are some genetic diseases—diseases caused by problems in genes.Today,scientists are looking for ways to cure genetic diseases by changing genes through a process called gene therapy.

1.What is DNA?

A.DNA is a kind of gene.

B.DNA is a substance that makes up genes.

C.DNA is the basic unit of heredity.

D.DNA is a measure to protect crime.

2.Which of the following about genes is correct according to the passage?

A.Plants,animals and human beings have the same genes.

B.Half people inherit all genes from their mother,others from their father.

C.Genes decide the trees shapes,the cats’ fur color and our eyes’ color as well.

D.Genes will give you a code when you need them.

3.An Austrian monk named Gregor Mendel .

A.first saw inherited patterns in people