对腹部实质性脏器病变，最简便易行的检查方法是（）。

A.X线摄片

B.CT扫描

C.同位素扫描

D.B超检查

E.纤维内窥镜检查

- Mr Smith, please teach me how to draw on the computer today.

- Oh, no._______. You have to get familiar with the keyboard first.

A．Learn to walk before you run

B．It's never too old to learn

C．A good beginning is half done

D．The early bird catches the worm