A:比热容、密度不变,热值减半
B:比热容、密度、热值均不变
C:比热容、密度、热值均减半
D:比热容减半,密度、热值不变
如图,OM是∠AOC的平分线,ON是∠BOC的平分线.
给出下列命题:
①“x2=1”是“x=1”的充分不必要条件;
②“x=﹣1”是“x2﹣3x+2=0”的必要不充分条件;
③命题“∃x∈R,使得x2+x+1<0”的否定是“∀x∈R,均有x2+x+1≥0”;
④命题“若x=y,则sinx=siny”的逆否命题为真命题;
其中真命题有____ .(把你认为正确的命题序号都填上)
对欧姆定律的理解,下列说法中错误的是
—Tell me something about your adventure in the rainforest, please.
— We lost our way in the forest and ___ made matters worse was ___ night began to fall.