According to the course, although psychological barriers are （）, they can be just as impenetrable as more obvious barriers, such as language differences.
A.stumble
B.invisible
C.intentionally
D.equipped
正确答案：B
According to the course, although psychological barriers are （）, they can be just as impenetrable as more obvious barriers, such as language differences.
A.stumble
B.invisible
C.intentionally
D.equipped
正确答案：B