Answer:
a. Option 3 best describes this statement.
This is because the option compares two different sets of employees receiving training and not receiving any training, it represents the case of an ideal randomized controlled experiment.
b. Option 2 best describes this statement.
This represents an observational cross sectional data set.
c. Option 1 best describes this statement.
This represents an observational time series data set because there are seven days track period of the employee.
d. Option 4 best describes this statement.
Since this represents a mixture of time series and cross sectional data set, it is panel data set.