What is a test tube commonly used for in scientific experiments?

A test tube is commonly used to hold liquids in scientific experiments. This cylindrical glass or plastic tube is designed to contain small volumes of liquid, making it ideal for mixing, heating, or reacting different substances. Its transparent nature allows scientists to observe the contents easily, and when combined with other laboratory equipment, test tubes facilitate various chemical analyses and experiments.

While holding gases, measuring time, and growing plants are also important tasks in scientific contexts, test tubes primarily serve the function of containing liquids, which makes option B the most accurate choice. Other equipment and tools are specifically designed for gas containment, time measurement, and plant growth.