请教语法２

窗UID: 209565

15. A challenging new area in inorganic chemistry is ---- the role of transition metals
in the biochemical catalysts called enzymes.
     (A) that of understanding
     (B) to have understanding
     (C) the understanding
     (D) understanding that
答案是Ａ，句子结构有点搞不懂

39. By 1810 the 23 towns of Hampshire County, Massachusetts, had reached a remarkable uniform of economic development as well as population density.
答案是Ｄ怎么不对了呢

40. With more than half the world's annual yield of 50 million tons of soy beans, an important source of protein, is grown in the United States.
答案是Ａ，怎么改呢

[ Last edited by 窗 on 2005-12-10 at 19:22 ]

lingpiaoUID: 2128680

that 指代 area

yxjessieUID: 194526

第二题不懂，第三题不要with吧。