Q.Which of the following pairs is correctly matched?

Step 1. Mammalia is mostly viviparous; only the small Prototheria group (e.g. the platypus) lays eggs, so 'always egg-laying' is wrong.

Step 2. Mammary glands are a defining mammalian feature, not found in Aves, so (b) is wrong; Amphibia has a three-chambered heart, not a four-chambered one, so (d) is wrong. …

Check each option's class-feature pairing against the correct defining feature of that cl …

• Assuming all mammals are viviparous without exception — Prototheria is a genuine, if small, egg-laying exception. …