Muscles contracting in inspiration

Steps:

• Inspiration requires diaphragm contraction to descend and increase thoracic volume.
• External intercostals contract to elevate ribs, aiding expansion.
• Internal intercostals relax to allow unobstructed movement.
• Match options to this pattern: diaphragm and external contract (✓), relax (×); internal contract (×), relax (✓).

Why B is correct:

• B accurately depicts diaphragm and external intercostals contracting (✓) while relaxing (×), and internal intercostals contracting (×) while relaxing (✓), aligning with respiratory mechanics where primary inspiratory muscles actively shorten.

Why the others are wrong:

• A: Erroneously marks diaphragm as contracting (×) and relaxing (✓), reversing its role.
• C: Incorrectly shows external intercostals relaxing (✓) and internal contracting (✓), inverting inspiratory actions.
• D: Fails to specify diaphragm relaxation properly and mirrors C's errors in intercostal roles.

Final answer: B