Poland’s core inflation plunged to the lowest level in five-and-half years in March, data released by the National Bank of Poland showed Tuesday. Inflation, excluding food and energy prices, slowed to 1% in March from 1.1% in February. The rate of growth was the slowest since September 2007, when prices advanced 0.9%. On a monthly basis, core consumer prices edged up 0.3% in February. At the same time, administrative prices increased 0.7% annually in March, and prices of the most volatile items rose by 1.5%. Poland’s consumer price inflation had weakened to 1% in March from 1.3% in February. Month-on-month, the consumer price index moved up 0.2%.