1. Introduction
2. Sample, Observations, and Data Reduction
2.1. Sample
2.2. Observations
2.3. Data Reduction
3. Data Analysis
4. Results
5. Discussion
5.1. The Comparison with Viscous Evolution Models
5.2. The Impact of Photo Evaporation and Variable Accretion
5.3. The Need to Account for Dust Evolution
5.4. Does the Mass Accretion Rate Decrease with Time?
6. Conclusions