The answer to this is D. The Thixotropic gel form is responsible for creating a barrier between the serum and the cells. This is known to be very helpful when contamination is being prevented. This will make it easier to remove whatever is contaminating the body. There are thixotropic fluids that are usually described as being thick.
They are so thick that they can barely flow. Some are specifically made that way while there are others that would need to be regulated so that they can flow more freely. Thixotropic fluids will only flow for a limited time. Once the time is up, it will go back to its usual thick form.