Concept:Vernier calipers are designed to measure internal dimensions precisely using their internal jaws.
Explanation:The inner diameter of a test tube is an internal measurement, so the instrument must have internal jaws specifically made for this purpose.
A micrometer screw gauge is best for external diameters and thin objects, not for internal cavities.
Pair of dividers can transfer measurements but cannot give a direct accurate reading.
A meter rule has too low a precision for measuring a small test tube diameter accurately.
A pair of vernier calipers has internal jaws that are inserted into the test tube to read the inner diameter directly and precisely.
Answer:D. pair of vernier calipers