Adjectives <> Adverbs - U5.1 grammar1, 2 and 3
Comparisons - U5.1 grammar1
Present Perfect <> Past Simple - U5.2 grammar 2, 3 and 4
Gerund - U5.4 grammar 1, 2 and 3 and U6.1 grammar 3
Who<>Which<>That<> 0 - U5.4 grammar 5 and 6 and U6.1 grammar 1 and 2
Must<>Have to<>Should<>etc. - U6.4 grammar1