Dr. cross is studying whether the psychological trait of dependency vs. independence changes as one gets older. he collects data from first, fourth, and ninth graders. dr. cross is studying the relationship between age and dependency/independence using research.

cross-sectional                              

Explanation:

Cross-sectional research: In cross-sectional research, the experimenter or the researcher examines a group of people, specific context, and a social phenomenon with the help of a sample. The cross sectional-study or research is also known as transverse study, prevalence study, etc. This is a type of an observational study, that examines a particular population data in a specific time.

Advantage:

1. Cost-effective

2. Easy to gather and assess data.

3. Less time taking.

In the give question, Dr Cross is studying the relationship between age and dependency/independence using cross-sectional research.

the period of human evolution has coincided with environmental change, including ('hominin' refers to any bipedal species closely related to humans – that is, on how do we know earth's climate has changed? a map showing dates and locations of prehistoric archeological sites and migration routes from africa into.

can you explain it better