1. Introduction  
2. Sample  
3. Observations and Data Reduction  
4. Results  
5. Discussion  
5.1. Gas-to-Dust Ratio and Determination of α  
5.2. Star Formation Efficiencies and Gas Depletion Timescales  
5.3. The $^{12}CO/^{13}CO$ Line Intensity Ratio  
6. Summary