It is accepted by everyone that knowledge is the most valuable _______ for human beings.( )
A.standardB.treasure
C.inventionD.instruction
These keys are ( )
she
hers
her
Johna soccer.( )
have
has
is
There are two in her family.( )
child
childs
children
I didn't know _____.( )
what we could do
how we could do
what can we do
How long is it since he _____this school?
He _____for three years.( )
has left; has left
left; has been away
leaves; has left