1. Introduction

2. Sample

3. Observation and Archive Data  
3.1. H I Observations Using the FAST  
3.2. HC₃N J=2·1 Observations of Nine PGCCs  
3.3. Archive Data of CO and Dense Gas Tracers  

4. Methods of Extracting HINSA  
4.1. Method 1  
4.2. Method 2  

5. Result  
5.1. CO Parameters  
5.2. Extracting HINSA  

6. Discussions  
6.1. CO and Dust Emission  
6.2. Morphologies and Environments of HINSA  
6.3. H I Abundances and Evolution Status  
6.4. Does the HINSA We Detected Trace Molecular Gas?  
6.5. HINSA and HC₃N  

7. Summary