Answer:
Verbs in -re
Step-by-step explanation:
Most verbs ending with -re will have a past participle ending in -u
Attendre - attendu (to wait, waited)
Battre -battu (to beat, beaten)
Défendre - défendu (to defend, defended)
But not all the verbs, some others are exceptions, like
Atteindre - atteint (to reach, reached)
French is famous for having numerous exceptions to rules. ;-)