Which of the following are the proper HTML tags used to create a numbered list?

a.

1. 
   
2. Item 1
3. 
   
4. Item 2
5. 
   
6. Item 3
7. 
   

b.

1. 
   
2. Item 1
3. 
   
4. Item 2
5. 
   
6. Item 3
7. 
   

c.

1. 
   
   1. Item 1
2. 
   
   1. Item 2
3. 
   
   1. Item 3
4. 
   

d.

1. 
   
2. Item 1
3. 
   
4. Item 2
5. 
   
6. Item 3
7.