These are hiatos with two of the same vowel in Spanish:
- ee: poseer
- ii: chiita
- aa: contraatacar
The meaning of hiatus is when two vowels are pronounced in different syllables.
In this case, the exercise presents hiatus with the same vowel two times. For example, "poseer" separated into syllables would be: po-se-er, so the two "e" are separated. The same happens with the other two examples given.