Which statement is supported by subsequent research?
piaget relied on case studies and child observations to develop his theory of psychosocial development.
piaget utilized an acceptable experimental design to test his cognitive development theory.
infants reach the stages of sensorimotor intelligence earlier than piaget predicted.
piaget accurately predicted the speed of infant cognitive development.

The correct answer is: Piaget utilized an acceptable experimental design to test his cognitive development theory.  

Explanation:

With this theory, Piaget stated that children develop cognitively through 4 stages.  

1. Sensorimotor stage (birth to age 2). Which is the one where children gather information from their senses (such as sight, smell, taste, touch, and hearing). That's why children in this stage are always touching things and taking them to their mouths. They're also very active, as they're discovering how to use their senses and also how to move their bodies.  

The main achievement during this stage is Object Permanence, this means that infants don't recognize the existence of an object even though they can't see it.

2. Preoperational stage (from age 2 to age 7). In this stage, children are developing their mental operation, such as imagination. So, during this stage children can think about things as symbols; you can notice that kids around 2 years old learn to talk, as they learn that words symbolize objects.

On the other hand, infants this age are very egocentric and that's because they have difficulties taking the points of view of others. For instance, if a 4-year-old is playing legos with you and throws one at your face, he won't understand he hurt you because this action didn't hurt him.

3. Concrete operational stage (from age 7 to age 11). This is where children learn the idea of conservation. Therefore, they understand that something can stay the same in quantity even though its appearance changes. An example is when you ask children what weighs more, a kilo of rocks or a kilo of feathers? They'll be able to answer that both weigh the same.

In this stage they're also able to solve math problems.

4. Formal operational stage (age 12+ - adolescence and adulthood). During this stage, children are able reason about abstract concepts and think about the consequences of potential actions and it's also where moral reasoning begins to take place, at this point children start reasoning more like adults and they continue to develop that over time.

In conclusion, this design is the most accurate to experiment on the cognitive development of children.