You are asked to study the causal effect of hours spent on employee training (measured in hours per worker per week) in a manufacturing plant on the productivity of its workers (output per worker per hour). Describe:

a. an ideal randomized controlled experiment to measure this causal effect;

b. an observational cross-sectional data set with which you could study this effect;

c. an observational time series data set for studying this effect; 

d. an observational panel data set for studying this effect.