Final answer:
The first part of the copypasta in base64 is Option A, which decodes to "Hello world!", a common starter phrase in programming.
Step-by-step explanation:
The question asks about the first part of a copypasta encoded in base64. Option A, represented as SGVsbG8gd29ybGQh, when decoded from base64, translates to "Hello world!" which is a common test phrase used in programming and often signifies the start of something, like a copypasta. Therefore, the correct choice would be Option A as it decodes to a meaningful phrase that could indicate the beginning of a text string or message.