Final answer:
Varying sentence structure and using effective transitions in an argument are important to make the ideas clear and keep the reader interested.
Step-by-step explanation:
In an argument, it is important to vary sentence structure and use effective transitions for several reasons. Firstly, varying sentence structure helps to make the ideas clear by avoiding repetitive or monotonous writing. Secondly, using effective transitions assists in keeping the reader interested and engaged by smoothly connecting ideas and showing the relationships between them.