In mid-December ,Australian students enjoy their (six-week-long) Winter holiday
这里是作为形容词使用的,所以必须是 数字-单位-形容
相当于 He is a 10-year-old boy.
十二月中旬,澳洲的学生可以享受六周的寒假.
放心,就是这里错了,其余都对的