---Lucy, is maths difficult to learn in a foreign school?

---I’m not sure, but no subject can be learned well __________hard work.

A．without

B．through

C．by

D．with

加大科技投入是提高农业产出的重要手段，下面做法体现了这一点的是 (    )

A．利用基因工程进行“无性杂交”，创造具有优良性状的新物种

B．由引水浇灌改为喷灌

C．多使用化肥、农药

D．采用传统的耕作方式进行粗放经营