This lesson was inconsistent as to whether a classifier was required (or I remain confused). As I recall, the picture choice just had 'khoác', and a permitted answer for 'dress' was 'đầm', but here the full 'áo khoác' was required. PLEASE tighten up the lessons on when English articles and Vietnamese classifiers are required.
As I understand it, classifiers are required if a specific things or things, but not required if it is a general concept. So I like meat (general), or I like the meat on the table? English and French and others all play a similar game I think? But not 100% sure on this.