Activity 1. Read and analyze the sentences. Select the letter of the correct answer in the box and write i the space provided. a. International 1. All movements are compared with a System of Units 2. The most commonly used frame of reference is b. Frame of 3. A change in position relative to a frame of reference is reference 4. is the length of the path between two points. Earth 5. The standard system of measurement is called d. distance e. motion