Question
Name the blank space a, b, c and d in the table given below:
| S.No. | Type of Microbe | Name | Commercial Product |
| 1. | Fungus | a | Penicillin. |
| 2. | Bacterium | Acetobacter aceti. | b |
| 3. | c | Aspergillus niger. | Citric acid. |
| 4. | Yeast | d | Ethanol. |