A:3种
B:4种
C:5种
D:6种
13–8 =____ 17–3 =____22+5 =____60+23 –3=____
43+ 20=____7+60=____68– 6=____88– 50+30 =____
88–7 =____ 6+9 =____13-9=____75–60+70=____
90–20= ____ 50+48 =____ 74–40 =____78–8–30 =____
49+ 40=____15–8=____ 30+60 =____32+50–40 =____
设z=1+i(i是虚数单位),则2z+z2等于( )
青蛙、家燕、小麦个体发育的起点都是受精卵。