遗传病是由于____ 或____ 等遗传物质的改变而引起的疾病.遗传物质的改变在染色体水平上表现为染色体____ 和____ 的改变.
15-7=( )
俗话说:“井无压力不出油,人无压力轻飘飘”。对这句话理解正确的是( )
若x,y满足约束条件x+y≥1x-y≥-12x-y⩽2,目标函数z=ax+2y仅在点(1,0)处取得最小值,则a的取值范围是( )
The book was written in _______ easy English _______ even primary school students could understand it.