描述某系统输出y1(t)和y2(t)的联立微分方程为
y'1(t)+y1(t)-2y2(t)=4f(t)
y'2(t)-y1(t)+2y2(t)=-f(t)
将下列DNA分子按熔链温度由低至高列序:
Ⅰ.A A G T T C T C T G A A
T T C A A G A G A C T T
Ⅱ.A G T C G T C A A T G C A G
T C A G C A G T T A C G T C
Ⅲ.G G A C C T C T C A G G
C C T G G A G A G T C C
若(a,b)=1,则T(ab)=T(a)T(b)(这里T(a)表示a的正约数的个数).
若(a,b)=1,则T(a+b)=T(a)+T(b)?
What a lovely day,______?
A.doesn’t it
B.isn’t it
C.hasn’t it
D.won’t it