Correct these sentences. Use full stops in sentences. Write the full variant:

1. The whole city was serious damaged.

2. The cake was surprising delicious.

3. Jean is a good athlete. He can run very fastly.

1. The whole city was seriously damaged.
Explanation: In this sentence, the word "serious" should be an adverb describing the verb "damaged." The correct adverb form of "serious" is "seriously." Therefore, we need to change "serious" to "seriously." The sentence should be: "The whole city was seriously damaged."

2. The cake was surprisingly delicious.
Explanation: In this sentence, the word "surprising" should be an adjective describing the noun "cake." However, in this context, we are describing the taste of the cake, not the act of being surprised. The correct adjective form of "surprising" is "surprisingly." Therefore, we need to change "surprising" to "surprisingly." The sentence should be: "The cake was surprisingly delicious."

3. Jean is a good athlete. He can run very fast.
Explanation: In this sentence, the word "fastly" is incorrect. The adverb form of "fast" is simply "fast." Therefore, we need to change "fastly" to "fast." The sentence should be: "Jean is a good athlete. He can run very fast."

Overall revised sentences:
1. The whole city was seriously damaged.
2. The cake was surprisingly delicious.
3. Jean is a good athlete. He can run very fast.