Which of the following motor achievements, on average, occurs last? a. rolls from back to side b. rolls from side to back c. sits up by himself or herself d. grasps cube

The best answer for this question would be:

C. Sits up by himself or herself 

This is the best motor achievement because, the baby can finally be able to balance itself and its body after rolling from side to side. The structure of the bones are finally strong enough and stable. 

Well, l think that some effective communication is, emotional barriers and lack of attention, interest distraction or irrelevance. also some physical disabilities such as hearing problems or speech difficulties.      l hope i am correct  and you good luck.