1._______ is the center of our planetary system was a diffic

1._______ is the center of our planetary system was a difficult concept to grasp in the Middle Age.
A) It is the sun and not the earth
B) Being the sun and not the earth
C) The sun and not the earth
D) That the sun and not the earth
2._______ it or not,his discovery has created a stir in scientific circles.
A) Believe
B) To believe
C) Believing
D) Believed
3._______ kinds of matter in the world.
A) There is a few million
B) That there are millions
C) There are a few million
D) It is millions
4._______ man can now create radioactive elements,there is nothing he can do to reduce their radioactivity.
A) As
B) Whether
C) While
D) Now that
5._______ me,I think an English-Chinese dictionary is much more helpful to our study than an All-English dictionary.
A) As far as
B) As far
C) As for
D) As regard
6._______ my return,I learned that Professor Smith had been at the Museum and would not be back for several hours.
A) At
B) With
C) On
D) During
7._______ of the burden of ice,the balloon climbed up and drifted to the South.
A) To be free
B) To free
C) Freeing
D) Freed
8._______ one time,Manchester was the home of the most productive cotton mills in the world.
A) On
B) By
C) At
D) Of
9._______ quite recently,most mothers in Britain did not take paid work outside the home.
A) Until
B) Before
C) From
D) Since
10._______ she first heard of the man referred to as a specialist.
A) That was from Stephen
B) It was Stephen whom
C) It was from Stephen that
D) It was Stephen that

C A D
A C C
D C B
D