Yes, you can use a variety of sentence types and sentence structures in the Writing section of the IELTS exam. This will not only demonstrate your language proficiency but also make your writing more engaging and coherent.

Importance of sentence variety
Using a variety of sentence types and structures is crucial for achieving a high score in the Writing section. It shows that you have a good command of grammar, vocabulary, and sentence construction. It also adds fluency and complexity to your writing, making it more interesting for the reader. Moreover, it allows you to convey your ideas more effectively, ensuring that your message is clear and well-developed.

Types of sentences
There are four main types of sentences that you can use in your writing:

1. Simple sentences: These consist of a single independent clause and express a complete thought. They are usually short and straightforward.
Example: "I went to the park and played basketball."

2. Compound sentences: These consist of two or more independent clauses joined together by coordinating conjunctions or semicolons. They allow you to connect related ideas and show the relationship between them.
Example: "I went to the park, and I played basketball."

3. Complex sentences: These consist of an independent clause and one or more dependent clauses. They allow you to express complex relationships between ideas, such as cause and effect or condition.
Example: "Although it was raining, I went to the park to play basketball."

4. Compound-complex sentences: These consist of two or more independent clauses and one or more dependent clauses. They combine the features of compound and complex sentences, allowing you to express multiple ideas and their relationships.
Example: "Although it was raining, I went to the park to play basketball, and my friends joined me later."

Sentence structures
In addition to using different sentence types, you can vary your sentence structures to add depth and sophistication to your writing. Here are some common sentence structures you can use:

1. Subject-verb-object: This is the most basic sentence structure, where the subject performs the action on the object.
Example: "She reads books."

2. Subject-verb: This structure consists of a subject and a verb, without an object. It is often used to express opinions or make general statements.
Example: "I agree."

3. Verb-object: This structure emphasizes the action being performed and is commonly used in passive voice constructions.
Example: "The book was read by her."

4. Conditional sentences: These consist of an if-clause and a main clause, expressing a condition and its potential result.
Example: "If it rains, we will stay indoors."

5. Inversion: This involves reversing the typical subject-verb order to add emphasis or create stylistic effects.
Example: "Never have I seen such a beautiful sunset."

Conclusion
Using a variety of sentence types and structures in the Writing section of the IELTS exam is highly recommended. It showcases your language skills and enhances the overall quality of your writing. By incorporating different sentence types and structures, you can effectively communicate your ideas, engage the reader, and increase your chances of achieving a high score.