Statistics show that from 2017 to 2018, unemployment decreased while inflation also decreased Which of the following is a valid reason behind these  a

Statistics show that from 2017 to 2018, unemployment decreased while inflation also decreased Which of the following is a valid reason behind these 

a. Aggregate supply curve shifted to the right, which caused the price level to decrease and national output to increase 

b. Aggregate supply curve shifted to the left, which caused the price level to increase and national output to decrease 

c. Aggregate demand curve shifted to the right, which caused the price level and national output to increase 

d. Aggregate demand curve shifted to the left, which caused the price level and national output to decrease