Working with 3rd person

I have this link to practise with the pronunciation of the 3 forms of the 3rd person in singular but remember I'm interested in the difference between these 2 groups:

• GROUP A: you add -s or-es and the number of syllables doesn't change; e.g. works, plays, studies, loves
• GROUP B: you add -s or -es and you pronounce an extra syllable /IZ/; e.g. finishes, fixes, practises

The difference between the pronunciation within the group A is not so important and to do it simpler remember to pronounce /s/ when the verb ends in /p/ or /k/, (like asks or stops) but most of the verbs have the pronunciation /z/.