求翻译：国外关于提高外语听力课堂有效性的研究开始于20世纪初，从20世纪60年代以来（特别是20世纪80年代）逐渐成为一种较为系统的教学理论，并且不断完善。是什么意思？

Hearing on the improvement of the foreign language classroom effectiveness study began in the early 20th century, since from the 1960s (especially in the 1980s) has gradually become a more systematic teaching of theory, and continuous improvement.

Foreign on the improvement of foreign language listening classroom effectiveness research, which commenced in early 20th century, from the 20th century since the 1960s (particularly in the 1980s) gradually became a more systematic and continued to improve the teaching theories.

Overseas about enhances the foreign language hearing classroom valid research to start in the beginning of the 20th century, (has been specially 1980s) becomes one kind of system gradually since the 20th century 60's the teaching theory, and consummates unceasingly.

Study on improving the effectiveness of foreign language listening teaching abroad began in the early 20th century, since in the 1960 of the 20th century (especially in the 1980 of the 20th century) is becoming a more system teaching theory, and constantly improve.

Overseas about enhances the foreign language hearing classroom valid research to start in the beginning of the 20th century, (has been specially 1980s) becomes one kind of system gradually since the 20th century 60's the teaching theory, and consummates unceasingly.