The photomicrograph shows a cross-section of two structures found in mammals, observed with a light microscope. Which row is correct?
- AW: artery, X: vein, feature: X contains cells with haemoglobinic acid
- BW: bronchiole, X: vein, feature: X contains cells with oxyhaemoglobin
- CW: trachea, X: artery, feature: the lumen of W allows air to pass through
- DW: vein, X: atrium, feature: W contains deoxygenated blood