The following table shows portion of a positional index:

Which document(s) (if any) match each of the following queries where each expression within quotes is a phrase query? At which positions do the queries match?

According to tutor, we're meant to use TF from Boolean model to rank the documents (apply Boolean model to the first part and then TF to the second part) but I'm not sure how to do this.

(i) Young adults are back at universities

(ii) COVID is back with a vengeance

(iii) When can businesses reopen in Australia during the COVID-19.

There is something wrong with this positional index. What is the problem?

Pn>; COVID Back Adult University Vengeance Young Australia Business Reopen Doc1: ; Doc2: ; Doc3: ; 1: 2: ; 3: 4: 1: 2: 3: 4: 1: 2: 3: 4: 1: 2: 3: 4:9,17,125,295; 1: 2: 3: 4: 1: 2: 3: 4: 1: 2: 3: 4: 1: 2: 4: 1: 3: 3: | 4: Pn>; COVID Back Adult University Vengeance Young Australia Business Reopen Doc1: ; Doc2: ; Doc3: ; 1: 2: ; 3: 4: 1: 2: 3: 4: 1: 2: 3: 4: 1: 2: 3: 4:9,17,125,295; 1: 2: 3: 4: 1: 2: 3: 4: 1: 2: 3: 4: 1: 2: 4: 1: 3: 3: | 4: