下列各式中,是3a2b的同类项的是( )
A:2x2y
B:﹣2ab2
C:a2b
D:3ab
“是挫折使骨头坚如燧石,是挫折是软骨变成肌肉。”这一外国格言表明( )
My parents ____ (marry) for 25 years.