Consider the following pairs:

Type of Unemployment	Feature
1. Frictional Unemployment	person seems visibly working but his marginal productivity is zero
2. Disguised Unemployment	When people are employed in the most productive and suitable roles, often reflecting optimal staffing
3. Technological Unemployment	men are replaced with machines
4. Structural  Unemployment	skill/qualification is insufficient for the jobs

How many pairs given above are correctly matched?