Statements:
Some letter are alphabets.
All alphabets are vowels.
Some vowels are consonants.
Conclusions:
I. Atleast some consonants are letters.
II. All vowels can be letters.
Some letter are alphabets(I) + All alphabets are vowels(A) ⇒ Some letter are vowels(I) + Some vowels are consonants(I) ⇒ No conclusion. Hence, conclusion I does not follow. Some letter are alphabets(I) + All alphabets are vowels(A) ⇒ Some letter are vowels(I) ⇒ Probable conclusion ⇒ All vowels can be letters. Hence, conclusion II follows.