— These problems are too hard to . Will you give me some advice? — There are many ways. The most important is to have a careful plan.
A:hand out
B:work out
C:look out
D:break out
李师傅每小时生产x个零件,10小时生产____个。
动物多样性的保护措施包括____、____、____.
如图,是二次函数 y=ax2+bx+c(a≠0)的图象的一部分,给出下列命题 :①a+b+c=0;②b>2a;③方程ax2+bx+c=0的两根分别为-3和1;④a-2b+c>0.其中正确的命题的个数是