Explanation:
The correct answer is option 'b) Unbaked bricks'.

Reasoning:
The walls of the new room are made with unbaked bricks, which means that the bricks used for constructing the walls were not baked in a kiln. Let's understand why unbaked bricks were used and why the other options are not correct.

Mud:
Mud is a common building material, especially in rural areas. However, mud is not a suitable material for constructing walls as it lacks strength and durability. Walls made of mud can easily erode or collapse, especially in rainy or humid climates. Therefore, using mud to construct the walls of the new room would not be a wise choice.

Bamboo sticks:
Bamboo sticks are often used for constructing temporary structures or as a supporting material in construction. While bamboo is lightweight and flexible, it is not suitable for building solid walls. It lacks the strength and stability required for long-lasting walls. Therefore, using bamboo sticks for the walls of the new room would not be a suitable option either.

Unbaked bricks:
Unbaked bricks, also known as sun-dried bricks or adobe bricks, are made by shaping clay into bricks and allowing them to dry naturally under the sun. These bricks are commonly used in regions where kiln-fired bricks are not easily available or affordable. Although unbaked bricks are not as strong as baked bricks, they still offer sufficient strength and durability for constructing walls. They are a suitable option for the construction of the new room.

Conclusion:
Considering the options given, it is clear that the correct choice for constructing the walls of the new room is option 'b) Unbaked bricks'. These bricks provide a reasonable level of strength and durability while being an affordable and easily accessible building material.