whiCh sEntEnCE BEst ExprEssEs thE mAin iDEA oF pArAgrAph 2
A．thE First sEntEnCE.
B．thE sEConD sEntEnCE AnD thE thirD sEntEnCE.
C．thE Fourth sEntEnCE.
D．thE lAst sEntEnCE.