In my puzzle you are requested to find two sets: the left hand set and the right set, fitting the following requirements:
1. LHS= (CITY, COUNTRY)
RHS= (names of 2 consecutive months)
2. The city and the country should be on the same continent.
3. The quantities of letters (consonants + vowels) in the sets need not be equal.
4. C1, C2, C3, … etc represent distinct consonants.
(Y, if present, should be considered a consonant.)

Examples:
If the sets were (Madrid, Romania) and (June, July),
then the puzzle would be posted as follows: LHS= (twice C1, twice C2, twice C3, C4 & some vowels) & RHS = (C4, twice C5, C6, C7 & some vowels).
Order of consonants is immaterial.
Another example:
If LHS=(Tallinn, Italy) & RHS=(September, October),
then the data in the puzzle would be LHS=(twice C1, thrice C2, twice C3, C4) & RHS=(twice C1, C5, C6, C7, C8, twice C9, twice C10).

The puzzle (extension)
Given two sets: LHS=(CITY, COUNTRY) & RHS=(2 consecutive months)
The 4 requirements in bolded text above apply to the following codes:
LHS=(C1, C2, C3, C4 and vowels) & RHS=C1, C2, C3, C4, C5 and vowels).

D2: Find one solution.
D3: Find three or more solutions.

HAVE FUN !