Which of the Following Better Explains 'Bottleneck Products

Which of the following better explains 'Bottleneck Products'? 

A)  These items represent a high value in terms of money but they are vulnerable with regard to their supply. They can only be obtained from one supplier. 
B)  These items represent a relatively limited value in terms of money but they are vulnerable with regard to their supply. They can be obtained from many suppliers. 
C)  These items represent a relatively limited value in terms of money but they are vulnerable with regard to their demand. They can only be obtained from one supplier. 
D)  These items represent a relatively limited value in terms of money but they are vulnerable with regard to their supply. They can only be obtained from one supplier.