题干

某学者欲研究被石油污染过的土壤中细菌数量,并从中筛选出能分解石油的细菌.下列操作错误的是(    )

A:利用平板划线法对细菌进行计数

B:以石油为唯一碳源的培养基筛选

C:采用稀释涂布平板法分离菌种

D:称取和稀释土壤样品时应在火焰旁

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A

同类题5

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    Many students want to give gifts to their teachers, and they often wonder what gifts to give to their teachers. After almost two decades as a teacher, here are some thoughts.

    First, not giving your teacher anything is perfectly fine. Teachers do not expect to receive a gift and are often surprised when they receive a gift. Believe it or not, the gift that a teacher receives (or does not receive) has no influence on his or her opinion of the child. No teacher will ever remember which child arrived at school with a gift and which did not. Trust me. In fact, many schools do not allow teachers to accept gifts from parents, so offering a gift can place a teacher in a difficult situation. As a result, no gift is sometimes just easier for a teacher.

    But if you're going to give your teacher a gift, here are a few suggestions:

    The best gift I ever received from students was given to me when my daughter was born. Each student in my class bought his or her favorite childhood book and signed the inside cover with a message to Clara. These books were then put into a library and gathered to me after Clara's birth. The books in that library are still some of Clara's favorites today, and we always take a moment to read the messages.

    Two things to take away from this: Books make excellent gifts. Gifts for a teacher's children make excellent gifts.

    But when it comes to gifts, I believe that the best gift that you can give a teacher is simply a note expressing your appreciation for all that he or she has done for you. I have letters from students that I appreciate (感激) as much as any other object in my life. I read these letters after difficult days in the classroom. They lift my spirits beyond measure.