September a changeling, busy a squirrel a hickory tree, idle a languid brook.九月真是变幻莫测, 忙来如山核桃树上的松鼠, 闲来却又象懒散缓流的小溪.September is a changeling busy as squirrel in a hickory tree, idle as a languid brook.九月忙来如胡桃树上的松鼠, 闲来如缓缓流淌...
A hydrocarbon was known to be either an alkene or alkane.某碳氢化合物已知可能是烯烃或是烷烃.The hydrocarbon must be an alkene.这个碳氢化合物必定是烯烃.The betaine will collapse to the alkene only when these two functions are eclipsed.只有当这两个基团移至重迭位置时...