ANSWER:
A) The developmental design that was used was CROSS-SEQUENTIAL RESEARCH DESIGN. Because the researcher has choosed to test different age groups (the same age in one group), at the same time. That means that children of 3, 4, 5 and 6 years old, Has been grouped according to their age difference and measured at the same time, as their are been followed up.
B) It will help the researcher to distinguish the difference in the emotional intelligence, among individual of the same age, and to relate the mean difference of the emotional intelligence of each age group to the other age group. This means it involves cross-sectional and longitudinal research design in it.
C) It is very expensive, and participants may loss interest in the long term.
D) The dependent variable in this research study is their EMOTIONAL INTELLIGENCE. This is because their emotional intelligence of the children tends to change with the ages of the participants and individual. This variable can be manipulated by the researcher, if he choose to change the age of the participants.
E) The subject variable in this research are the AGES of the participants. Their age are the subject because it can not be changed or manipulated by the research.