English GrammarMaths,one of the most important subjects,___

choose A
‘one of the most important subjects’is parenthesis.So we can simplify the sentence like this.Maths ___ insterested him.
So‘interested’should be the passive form of interest and we should choose A.The whole sentence means在几个很重要的科目里,数学深深地吸引着他.But if you want to use “is”,you should say ‘He is always interested in maths which is one of the most important subjects’

B.is
这是个被动句，表示被他感兴趣。
全句“Maths, one of the most important subjects, is always insterested him”即是“玛斯，这是他总是感兴趣的最重要的事情之一。”

interested adj.有兴趣的，感兴趣的
be interested in sth 对某事物感兴趣。
如为 interest vt.使……发生兴趣的 被动形式为interested
整句翻译为：
在几个很重要的科目里，数学深深地吸引着他。/他对数学最感兴趣。
数学作为单数第三人称，应使用has
选A...