1 ____widely used in the chemical industey ,sodium carbonate is prinicipally consumed by the industey.
A) Despite
B) Though

2 Helium is not flammable and, next to hydrogen, is____
A)kmown the lightest gas
B)the lightest gas known

１．选Ｂ
despite不管，尽管．是介词,后加名词,或动名词，一般不接过去分词的形式
in despite of　固定搭配，不管，尽管
eg.Despite the bad weather,they had a good time.
though是连词,虽然,尽管，后接句子．widely used in the chemical industey 在这里是省略了主语 it is/sodium carbonate is ,因为主句和从句是同一主语，所以从句的主语可以省去
eg.Though it was cold,they had a good time.
though (Tom was)young,Tom was good at doing this work.
这句话的意思是，虽然碳酸钠被广泛应用于化学也，但它主要在工业中使用

２．选Ｂ
known是过去分词做后置定语，也可以看做省去了which is,被知道
Helium is not flammable and, next to hydrogen, is the lightest gas
which/that is known.
如选Ａ　必须加kmown as the lightest gas
know as...固定搭配，称为，被认为