Answer: Option (b) is correct.
Explanation:
During extreme dry periods, there will be either very less availability of water or no water at all.
Hence, the tortoises avoid excretion as a watery waste at any time because they are not getting enough water from their surroundings.
Thus, at this period of time the waste eliminates as a white paste.
Therefore, during extreme dry periods tortoises will eliminate waste as a white paste.
