My life will be ________ better than she is now.[ ]
A. a lot
B. a lot of
C. a few
D. more
答案:A
已知在1×105Pa,298 K条件下,2mol氢气燃烧生成水蒸气放出484 kJ热量,下列热化学方程式正确的是[ ]
A.H2O(g)=H2(g)+1/2O2(g)△H = +242kJ/mol
B.2H2(g)+O2(g)=2H2O(l)△H = -484kJ/mol
C.H2(g)+1/2O2(g)=H2O (l)△H = -242 kJ/mol
D.2H2(g)+O2(g)=2H2O(g)△H = +484 kJ/mol
若二次型f(x1,x2,x3)=x21+2x32+x23+2x1x2+2tx2x3是正定的,则t的可能取值范围是()。