DNA诱变有哪些种类，各有何特点？

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One day when I was five years old , my mother was washing the kitchen floor. I was telling her about a new girl at school, and she looked up at me and said, “__1___are your two best friends?”
I was not __2___ what to say, “Um--- Jenny and Mary.”
My mother __3___ washing the floor and asked me, “ Well, what about Kate and Cindy?”
“But they’re my __4___.”
“Yes, but they can __5___ be your best friends. Friends may come and __6___, but your sisters will always be there for you.”
At that time I felt __7___. How could my two sisters be my closest friends? We fought all the time over toys, food, and what to __8___ on TV. How could my sisters be my best friends? They weren’t even the same age as me. We all had our own ___9__ at school. But my mother never let us _10___ that sisters are lifelong friends. Like all mothers, she wanted to give us a great gift ___11__ let us know how lucky we were. She let us play together and always punished us in the same way, too.
We didn’t always __12___ well and fought just like any other sisters. Now twenty years have __13___. We realise that our mother is __14___. Today I share things with my sisters that I don’t ___15__ with anyone else.

小题1: A．What B．Who C．Where D．Which

小题2: A．sure B．able C．sorry D．afraid

小题3: A．began B．stopped C．suggested D．practised

小题4: A．sisters B．brothers C．friends D．classmates

小题5: A．ever B．never C．still D．already

小题6: A．go B．stay C．live D．follow

小题7: A．sad B．great C．relaxed D．strange

小题8: A．do B．play C．listen D．watch

小题9: A．coaches B．teachers C．students D．friends

小题10: A．think B．know C．forget D．remember

小题11: A．and B．but C．so D．or

小题12: A．get off B．get down C．get along D．get together

小题13: A．wasted B．lost C．passed D．finished

小题14: A．tired B．right C．wrong D．dead

小题15:. A．help B．share C．make D．care