The figure given below shows a small part of human lung where exchange of gases takes place. Select the option which represents labelled part (A, B, C or D) correctly identified along with its function.

(A)C : arterial capillary - passes oxygen to tissues
(B)A : alveolar cavity - main site of exchange of respiratory gases
(C)D : capillary wall - exchange of O2 and CO2 takes place here
(D)B : red blood cells - transport of CO2 mainly.

The NCERT line that answers it

Verbatim line

Alveoli are the primary sites of exchange of gases.

Chapter: Breathing and Exchange of Gases
Section: 14.3 EXCHANGE OF GASES
Page: 6
Words matched: 9 of 9

The answer appears as a continuous sentence in NCERT. This is that sentence.

How this line gives the answer

0, emb=1.0, combined=1.0). Verified: high — The span 'Alveoli are the primary sites of exchange of gases' directly and conclusively states that the alveolar cavity (A) is the main site of gas exchange, which matches option B exactly.

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