—I can't find my pet cat everywhere.
—Sorry to hear that.You be very worried.
A:should
B:must
C:may
D:will
That is my father, that is my mother, and that is me. We are in a happy .
已知某种限制性内切酶在一线性DNA分子上有3个酶切位点,如图中箭头所指。如果在该线性DNA分子在3个酶切位点上都被该酶切断,则会产生a、b、c、d四种不同长度的DNA片段。现有多个上述线性DNA分子,若在每个DNA分子上至少有1个酶切位点被该酶切断,则从理论上讲,经该酶酶切后,这些线性DNA分子最多能产生长度不同的DNA片段种类数是( )
在人造卫星上,利用的能量来源主要是( )
世界上降水量最多的地方是:( )