A.I. Explanation:

Correct answer: shelters

Explanation: The word 'shelters' fits grammatically as it is a verb in the present tense that aligns with the subject 'the ribs,' indicating an action that the ribs perform. Contextually, it conveys the idea of providing protection, which is consistent with the overall theme of the passage regarding the protective functions of bones.

Meaning: 'Shelters' means to provide protection or cover for something, in this case, the heart and lungs.

Wrong options:

• displaces: Displaces means to move something from its place, which does not convey the protective function intended in this context.
• envelopes: Envelopes suggests wrapping something completely, which is not the precise action of the ribs as they provide a cage-like structure rather than a complete wrap.
• hurts: Hurts indicates causing pain, which is the opposite of the intended meaning of protection in this context.

Correct answer: two

Explanation: The word 'two' is the correct numeral that indicates the quantity of bones meeting at a joint. It fits grammatically as a cardinal number and contextually as it accurately describes the typical number of bones that form a joint, aligning with the passage's focus on anatomy.

Meaning: 'Two' refers to the number 2, indicating that typically two bones come together at a joint.

Wrong options:

• to: To is a preposition that does not indicate quantity and does not fit the context of counting bones.
• too: Too is an adverb meaning excessively, which does not apply in this context where a specific number is needed.
• too many: Too many is a phrase indicating an excessive quantity, which contradicts the straightforward count of bones at a joint.