Answer, and give a reason. Why does milk added to tea right away keep the tea warmer than milk…

Step 1. (a) Milk first lowers the temperature at once, and the cooler tea then loses heat more slowly, because the rate goes as the excess.

Step 2. (b) The lid stops evaporation and convection from the surface, so $k$ is smaller.

Step 3. (c) No. Once it reaches room temperature, heat stops flowing.