Big Ben is not the name of a man. It's the name of a big clock in London. This clock has four faces. So, no matter(无论)where you stand, you can read the time on the face of Big Ben. Each face is the size of a bus. The hands are about four metres long. If you go to London, you may want to visit the Houses of Parliament(英国国会大厦). In that place you will find Big Ben sits at the top of the clock tower in the Houses of Parliament. You will probably hear it and see it. The big clock makes such a loud noise. It goes every quarter of an hour. Big Ben has been the most famous symbol(标志)of  London

目前，港澳地区与珠江三角洲地区的经济合作模式是（    ）
①港澳地区——“前店”     ②珠江三角洲地区—“后厂”  
③珠江三角洲地区—“前店” ④港澳地区—“后厂”

明代《二如亭群芳谱》一书中写道：“西番葵，茎如竹，高丈余，叶如蜀葵而大。花托圆二三尺，如莲房而扁。花黄色，子如草麻子而扁。”“西番葵”后来成为我国主要农作物之一，得益于（    ）