input: Write a python function to filter rows of a DataFrame where the population is higher than 500 million.
  assert filter_large_countries(df).equals(pd.DataFrame({'Country': ['China'], 'Population': [1400000000], 'Area': [9596961], 'GDP': [14140163]}))
output: def filter_large_countries(df):
      return df[df['Population'] > 500000000]