to such an extent相當于so muchit litters up her desk to such an extent that every time she opens it, loose bits of paper fall out in every direction.= it litters up her desk so much that every time she opens it, loose bits of paper fall out in every direction.that之后是結果狀語從句the air pollution is so serious to such an extent that some freeways have been put out of use結構上沒有問題,但是意思上好像略有點累贅（so 和to such an extent）,不過應該沒事