Hello, I need a better understanding of costing methods. Could you please help answer the following questions?

Companies can choose from different costing methods: process/product costing and activity-based costing.What are some ABC cost drivers the company might use and how could the costs differ if one method is chosen over the other?

Why are units often in different stages of completion with respect to raw materials and conversion costs?

Do transferred-in costs occur in all departments of a manufacturer?

Thank you for your help!