What are the answers to questions 9, 10, and 11 regarding agriculture and farming practices?

Here are the answers to the questions:

9. Kevin wants to conserve soil nutrients. Which practice should she avoid?
Monocropping involves growing the same crop repeatedly on the same land, which depletes specific nutrients and degrades soil health over time. Practices like crop rotation, composting, and using organic fertilizers help conserve soil nutrients.
The correct option is B.
$\boxed{\text{B. Monocropping}}$

10. Kimani wants to practice agroforestry. Which benefit can he expect from growing trees on his farm?
Agroforestry integrates trees into farming systems. Trees help improve soil structure by their root systems binding soil particles, increasing organic matter, and enhancing water infiltration. They also reduce soil erosion and often increase biodiversity. Reduced crop yields are generally not an expected benefit; rather, overall farm productivity can improve.
The correct option is C.
$\boxed{\text{C. Improved soil structure}}$

11. Mwema wants to construct a poultry fold. He is expected to use all the following materials except one. Which one?
Nails, wood, and wire mesh are common and essential materials for constructing a poultry fold (for framing, fastening, and enclosure). Stones are generally not a primary construction material for the main structure of a poultry fold, although they might be used for a foundation or flooring in some cases.
The correct option is D.
$\boxed{\text{D. Stones}}$

12. Soap remains a relevant cleaning product because it is;
Soap is widely used because it is an effective cleaning agent, generally affordable, and can be used for various cleaning purposes (versatile). It is not primarily known for being expensive or luxurious for general use.
The correct option is B.
$\boxed{\text{B. effective, affordable and versatile}}$