Final answer:
When heating liquids in a test tube, it is important to position the test tube vertically in a test tube holder.
Step-by-step explanation:
When heating liquids in a test tube, it is important that the test tube be positioned vertically in a test tube holder. This helps to prevent the liquid from splashing out or bubbling over. By keeping the test tube upright, the liquid can evenly distribute heat and boil without causing any accidents or spills.