Which sentence is correct?

There are all kinds of self/service vending machines in Japanese cities.

There are all kinds of self-service vending machines in Japanese cities.

There are all kinds of self service vending machines in Japanese cities.

the 2nd one

Explanation:

i took the test

The correct answer is "There are all kinds of self-service vending machines in Japanese cities"

Explanation:

A sentence is considered to be correct if all the elements in it are written correctly and the general sentence follows grammatical and language conventions. In the case presented, the sentence "There are all kinds of self-service vending machines in Japanese cities" is the correct sentence because different from other options the term "self-service" has been written correctly. This can be explained as this term is a compound adjective that includes an adjective (self) and a noun (service), and according to grammar these type of words should be hyphenated (-) because they form a unit which means is a single term that derives from the combination of both words.