The correct answer is D. no article.
The word "seaside" is a common noun, which means it refers to a general place or thing. Common nouns are not typically preceded by articles.
In this case, the speaker is not referring to a specific seaside, but rather to the general concept of a seaside. Therefore, no article is needed.
Here are some other examples of common nouns that are not typically preceded by articles:
- city
- country
- park
- school
- hospital
- library
- museum
- beach
- mountain
- river
- lake
- forest
- desert
- ocean
Note that there are some exceptions to this rule. For example, if the speaker is referring to a specific seaside, such as "the seaside in California," then an article would be needed.
