Helen's Daughter Started to Walk Holding onto Furniture at 7

Helen's daughter started to walk holding onto furniture at 7 months of age, while Cathy's son started to walk holding onto furniture at 12½ months of age. How should Helen and Cathy respond to their children's abilities?

A) Helen should be happy that her daughter's development is more advanced than the majority of children at the same age, and Cathy should be worried because her son is walking much later than would be expected.
B) Helen should try to stop her daughter from walking because she is walking earlier than would be expected for her age; Cathy should be happy that her son is starting to walk at the age that would be expected.
C) Both Helen and Cathy should be worried because their children are starting to walk holding onto furniture much later than would be expected.
D) Both Helen and Cathy should be happy with how their children are developing because they are walking holding onto furniture within the range of ages found to do so in a national study.