German A2 Level Question

Option 'b' correctly uses 'maximum' to describe the greatest amount that can be carried. In 'a', 'maximum temperature' is typically used to describe a high, not cold temperature. 'c' incorrectly uses 'maximum' with 'tired' as it should describe a measurable amount. 'd' would be better with 'maximum effort' or 'maximum capacity' instead of speed, though the usage can be contextually correct.