2014年6月英语四级作文真题附范文(第2套):A Beautiful City in China

作者词汇表达较丰富准确，不过高级词汇的积累还有很大的空间；文章采用了适当的过渡词和衔接词，结构比较严谨；若增加一些从句的使用，文章会更不错。

It is widely believed that the drop in the selectivity to SC at higher temperature is due to the exothermic nature of coupling reaction, which leads to the copolymerization of SO with CO2 and thus gives by product such as polystyrene ether [46]. The 1H-NMR spectra of the crude products obtained at 120 oC using ZnBr2/Fe3O4@MCM-41 [25] and Cu(acac)2/n-Bu4NBr/Fe3O4@MCM-41 as catalyst are given in Figs. 7a and 7b, respectively. The characteristic signal at δ=3.6 ppm assigned to polystyrene ether [6,47] presents in the former (Fig. 7a) while it is very weak in the latter (Fig. 7b). It is another explanation for no obvious change in the selectivity to SC in this work.