Immediate cause of the disease is

The correct option is C Both (a) & (b)
Immediate is the primary cause of the disease. Hence, it is also known as the first level of cause. For example organisms that enter our body and cause the disease are termed as an immediate cause. For example, virus, bacteria, protozoa etc.
The secondary factors which led these organisms enter our body are termed as a contributory cause. For example, dirty water, contaminated food, improper nourishment, poor standard of living, etc.