Parallel Construction/paralel structure

In English, every word in a sentence should be structured in such a way as to be equal and harmonious structure; a noun followed by a noun, the adjective followed by an adjective, and so on.

note the example below:

1. Parallel the noun:

I like Russian, German, Spanish and French.

In the sentence above, the underlined word is a noun, so the sentence is parallel.

Structure is wrong:

I like Russian, German, Spanish, and Diving

In the sentence above, Diving is V-ing, not a noun so the above sentence is not parallel.

2. Parallel adjectives:

Your home is big, beautiful, and comfortable

In the sentence above, the underlined word is an adjective, so it is parallel sentences.

Structure is wrong:
Your home is big, beautiful, and close by downtown.

Close by is a downtown-phrases, parallel structures should not be part of speech 2. Everything must adjective in this case.

3. Parallel to the verb:

He does exercises, reads a book, a radio listens. (PARALLEL)

He does exercises, reads a book, and listening a radio (NOT PARALLEL)

Equivalent connecting words such as and, as, or. and the like but unequal, than using parallel structure.

I want to study German or (to) study Greek (PARALLEL)
The word ‘to’ in parentheses are optional, may not be worn.