Final answer:
The correct interval over which both functions are positive is (0, [infinity]).
Step-by-step explanation:
To determine over which interval both functions are positive, we need to consider the given information about the functions' behavior. According to the options provided, we can analyze the descriptions and eliminate the options that do not match the given criteria. Based on the description of the functions, option B, (0, [infinity]), is the correct interval where both functions are positive. In this interval, the functions start at zero with an upward slope that increases in magnitude until it becomes a positive constant.