It is( ) that radio is broken ,for the sound given out is not( )Asure pure Bobvious;clear
Cclear;aloud Dcertain;loudly 解析为；有形式主语It可知第一空不能用sure,第二空只能用clear,aloud和loudly都是副词.为什么有It第一空不填sure,为什么副词就不能用在第二空?