Final answer:
The group 'c. cattle, city, metal' exhibits significant differences in pronunciation between American and British English due to the American tongue flap, which makes the 't' sound more like a soft 'd'.
Step-by-step explanation:
The question concerns differences in pronunciation between American and British English, specifically involving the occurrence of a tongue flap. The groups of words given are evaluated to determine where the differences are most noticeable. The tongue flap typically refers to a sound made when the tongue taps the roof of the mouth quickly, and this feature is common in American English but less so in British English.
In the given options, the group of words where a tongue flap creates a significant difference between American and British pronunciations would be c. cattle, city, metal. In American English, the 't' in these words is often pronounced as a quick tap of the tongue, known as a 'flap t', which makes it sound more like a soft 'd'. In British English, the 't' is usually pronounced clearly as a 't' sound.
In the word cattle, the 't' in American English might sound like a 'd', making it sound akin to 'caddle'. Similarly, for city, it would sound closer to 'cidy', and in metal, it would be like 'medal' when spoken in American English with a tongue flap.