求教prep2012上的一道sc题～～

Joaluo

Prep2012-Pack1-SC-009            VSC002452        EASY

Roughlytwice each centurythe planet Venus passesbetween the Earth and the Sun, an occasionknown as a transitof Venus, during which it makes the outline of the planetvisible in stark relief.

A.           during which it makes the outline of the planet

B.           during which the outlineof the planet becomes

C.           so that it makes the outlineof the planet

D.          such that duringwhich the of the planet becomes

E.           such that the outline ofthe planet becomes

刚刚看了prep解析，但对它的解析还心存疑虑：

1. 关于c/d/e选项的错误，解析说是因为so that和such that跟在了同位语“an occasion known as a transit of Venus”后面，造成指代不清。想知道这里的指代不清跟同位语有什么关系？

2. 解析说so that和such that错在强调了不必要的因果关系，那么在说明因果关系的时候，so that和such that用法和意思上有什么区别吗？

求各路大神指教～

Joaluo

Thanks!
但还有个问题，prep解析关于这题c选项的解释是 “The causal conjunction so is confusing when it immediately follows the appositive phrase an occasion known as a transit of Venus.”
解释中特别说了appositive。连词so和同位语有什么关系？