We want to analyze the evolution of the imports of an OECD country. To that end, the file p34.wf1 disposes information about the following variables:
Imports: imports of goods of country 
GDP: Gross Domestic product of the country
RER: effective real exchange of the country currency versus the rest of the currencies.
OCP = number of occupied population
ND= National Demand of the country (sum of Consumption and Investment)
The available sample covers the period 1970:1 hasta el 2000:4. 
You should model the import function by using the previous information.