Final Answer:
If no Z is supplied in the substr (X, Y, Z) function, the correct behavior is "The function returns the substring starting from position Y to the end of the string X". Option C is the answer.
Step-by-step explanation:
In the substr (X, Y, Z) function, when the length parameter Z is omitted, the function assumes that the substring should extend from the starting position Y to the end of the string X. This behavior is useful when the developer wants to extract a substring without specifying the exact length, letting it go up to the end of the original string.
Option 1 suggests an error, which is incorrect; the function typically handles the absence of Z by defaulting to the end of the string. Options 2 and 4 provide inaccurate descriptions of the function's behavior.
Option C is the answer.