the two things ( ) Marx was not sure were the grammar and some of the idioms of english

the two things ( ) Marx was not sure were the grammar and some of the idioms of english
the two things ( ) Marx was not sure were the grammar and some of the idioms of english

the two things ( ) Marx was not sure were the grammar and some of the idioms of english
about which
The two things about which Marx was not sure were the grammar and some of the idioms.马克思不大有把握的两个方面是语法和某些习惯用语.