是老师要求阅读的一篇外文文献，但是由于目前计量经济学等知识还没有学，所以文章中有一些地方看不懂，所以想求助翻一下，以下是求助翻译的句子      1.All futures prices are taken from Thomson Reuters Datastream and are quoted in US-cents per bushel (corn and soft wheat) and pound (cotton), respectively.4 More precisely, all nearby futures series are constructed by rolling over on the same day that the previous contract expires.     这句话中尤其不明白roll over 是什么？         


2.。In an attempt to examine the short-run effects among agricultural futures markets, we have to assure that these markets do not exhibit co-movements in the long-run. Otherwise, we have to account for deviations of the long-run errors in our VAR framework and therefore estimate a vector error correction model (VECM). To check for the existence of a pairwise long-run relationship between futures prices for corn, cotton, and wheat, we have applied three different test procedures, viz. the unrestricted Johansen, 1988 and Johansen, 1991framework, the two-step Engle and Granger (1987) methodology, and the threshold cointegration approach proposed by Enders and Siklos (2001).6 The resulting test statistics are reported in Table 2 and clearly confirm that the null of no cointegration cannot be rejected in any case. Thus, we feel legitimized in proceeding by estimating VAR models in first differences, i.e. using the return series.
能不能翻译一下这整段呢...


3.原文中2.2. Empirical framework  这一整个部分能不能翻译一下。。原文地址：http://www.sciencedirect.com/science/article/pii/S0264999313003969

谢谢大家啦