Each cell in the human body contains about 25,000 to 35,000 genes, which carry information that determines your traits. Traits are characteristics you inherit from your parents; this means your parents pass some of their characteristics on to you through genes. For example, if both of your parents have green eyes, you might inherit the trait of green eyes from them. Or if your mom has freckles, you might inherit that trait and wind up with a freckled face. And genes aren’t just in humans — all animals and plants have genes, too.
Genes hang out all lined up on thread-like things called chromosomes. Chromosomes come in pairs, and there are hundreds, sometimes thousands of genes in one chromosome. The chromosomes and genes are made of DNA, which is short for deoxyribonucleic acid.
Chromosomes are found inside cells, the very small units that make up all living things. A cell is so tiny that you can only see it through the lens of a strong microscope, and there are billions of cells in your body. Most cells have one nucleus. The nucleus, which is sort of egg-shaped, is like the brain of the cell. It tells every part of the cell what to do. How does the nucleus know so much? It contains our chromosomes and genes. Tiny as it is, the nucleus has more information in it than the biggest dictionary you’ve ever seen.
71. What is the best title of this passage?
A. What Is a Gene?                    B. How Do Genes Work?
C. What Does A Gene Consist of?         D. How Do Nucleus Command Cells?
72. What does the underlined word “inherit” probably mean in the first paragraph?
A. carry          B. send        C. obtain           D. pass
73. Which of the following is NOT true according to the passage?
A. The parents pass some characteristics on to their children.
B. All living things receive traits from the old generations.
C. One’s green eyes might be passed on from the parents.
D.A mother’s freckled face might affect her young’s face.
74. From the passage we can know that______________.
A. genes can decide all your characteristics from parents.
B. genes exist inside cells that make up all living things.
C. genes tells every part of the cell what to do .
D. Chromosomes come in pairs containing genes.
75. From the passage we can conclude that ___________.
A. not all cells have one nucleus inside .
B. not all living things are made up of cells.
C. genes aren’t in humans but in animals and plants.
D. DNA is made of chromosomes and genes.