小周同学在探究“凸透镜成像规律”实验时，在光屏上得到清晰的与烛焰等大的像（如图）。保持凸透镜位置不变，为了在光屏上得到清晰的缩小的像，他必须

老王计划在他的菜园里种上白菜，已知他的菜园为长方形，长为9米，宽为6米，白菜每平方米大概可种植25颗，他可以种多少颗白菜？

    Last year I had a trip to Beijing with my parents. We visited many places of interest there. And there is lots of delicious food in Beijing, e____Beijing Duck. So we had it for s____ on the first day there. It____(taste)so delicious. I think it's really a Chinese t____We had a good time there for five days. We all think Beijing is well worth ____(visit).

我会辨字组词。

咏____          妆____            裁____          滨____  

泳____          壮____            栽____          缤____

下列有关硫铁矿制硫酸的说法中，正确的是(  )