Final answer:
The signs for 'grandmother' and 'grandfather' in ASL have an extra movement to indicate 'one generation back' from the signs for 'mother' and 'father'.
Step-by-step explanation:
The signs for 'grandmother' and 'grandfather' in American Sign Language (ASL) are related to the signs for 'mother' and 'father' through an extra movement that indicates 'one generation back' from the signs for 'mother' and 'father'. This extra movement represents the relationship between parents and grandparents, showing that they are one generation apart. The handshapes and motions used in the signs for 'grandmother' and 'grandfather' are different from the signs for 'mother' and 'father', so option c) is the correct answer.