人的手被热水烫了,在缩手的同时感到又烫又疼,以下说法不正确的是( )
A:这是反射活动
B:受到人体神经系统的调节
C:反射活动只受到脑的调节
D:完成反射的神经结构是反射弧
玉米种子中的胚乳属于胚。( )
Today is my birthday. I am a girl. My name is Han Mei. I'm nine years old. I have a birthday party. I have a birthday cake and many gifts. My father and my mother say“Happy birthday!”to me. I'm very happy.
下列命题中:①命题p:“∃x∈R,使得x2-1<0”,则¬p是真命题.②“若x+y=0,则x,y互为相反数”的逆命题为假命题.③命题p:“∀x∈R,x2-2x+3>0”,则¬p:“∃x∈R,x2-2x+3>0”.④命题“若¬p则q”的逆否命题是“若p,则¬q”.其中正确命题的个数是( )