A:look
B:look at
C:look after
D:look out
Here is a book, but it isn't _________.
40+2= 70+3= 10+8= 80+0= 40+5=
3+90= 10+6= 30+2= 50+9= 9+80=
1+10= 8+80= 20+1= 20+3=
0+10= 18–8= 86–6= 68–8= 65–5= 55–50= 93–90= 35–5= 45–40= 75–70= 38–30= 27–20=
57–7= 37–7= 100–30= 66–6=
43–3= 94–90= 34–30= 89–9= 51–1=
下列生物中,属于单细胞生物的是( )
实行计划生育后,我国每年新增人口数仍然很大,其根本原因是( )