4. The baby is very ...

Step 1: Analyze the sentence. 'very' often precedes a positive adjective or a superlative adjective. Step 2: Consider the options: 'pretty' (positive), 'prettier' (comparative), 'the prettiest' (superlative). Step 3: 'very' can be used with superlatives to emphasize them, but here it modifies 'pretty' to indicate a high degree of prettiness.

a) pretty