What do stages 'X' and '3' represent in the provided diagrams of a housefly life cycle and a human respiratory system cross-section, respectively?

Here are the solutions for the questions from the image:

9. The stage "X" on the life cycle below represents:
The life cycle of a housefly involves complete metamorphosis, which typically includes four stages: Egg, Larva, Pupa, and Adult (Imago). Following the sequence shown in the diagram: Egg $\rightarrow$ X $\rightarrow$ Pupa $\rightarrow$ Housefly (Adult). Therefore, stage "X" represents the larval stage.

The correct option is D. Larva.

10. The diagram below is a cross section of part of the respiratory system in man.
The structure labelled 3 represents:
In the human respiratory system:

• Structure 1 is the Trachea.
• Structure 2 represents the main Bronchus, which branches off the trachea and enters the lungs.
• Structure 3 represents the smaller branches that further divide within the lungs from the bronchi. These are the Bronchioles.
• Structure 4 points to even finer divisions or possibly the alveolar ducts/sacs.

The correct option is B. Bronchioles.