已知x+y=5,xy=3,那么
①x2+y2=( );
②(x﹣y)2=( )。
(1)19;
(2)13。
_______ is known to everybody, the moon travels around the earth once a month. .
A.It
B.As
C.That
D.What
高炉煤气中可燃气体含量最多的是()。