You don't have to install this radio in your new car; it's an ______ extra.
A. excessive
B. optional
C. additional
D. arbitrary
According to the passage, left-handedness ______.
A. is discouraged but not discriminated against
B. has caused discrimination as serious as sexism and racism
C. is a subject that has drawn more and more attention
D. is an advantage in running for public office
The word "accumulated" in line 6 is closest in meaning to（）
A. spread out
B. changed
C. became denser
D. built up
在世界众多的港口中，年吞吐量曾超过1 000万公吨的港口有100多个，其中( )以上集中在发达国家。
A. 60%
B. 70%
C. 80%
D. 90%
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