According to structure, Sentences are of __________ types.

Sentence structures
There are three types of sentence structures: simple, compound and complex.

1. Simple sentences
Simple sentences have only one main clause:
Example: We’re going on holiday tomorrow. (one main clause)

2. Compound sentences
Compound sentences have two or more main clauses, joined by a coordinating conjunction:
Example: I phoned her but she wasn’t there.

3. Complex sentences
Complex sentences have a main clause and one or more subordinate clauses, introduced by a subordinating conjunction.
Example. You can call me if you have any problems.

Source: Cambridge dictionary.