The process of cultural assimilation was a much easier process for people immigrating from:

The correct answer is D. Germany.

Cultural assimilation is often easier for immigrant groups whose language, customs, and cultural practices are more similar to those of the host country. In the case of the United States, German immigrants often shared similar cultural values, religious practices, and were more likely to speak languages related to English, making their integration smoother compared to immigrants from Egypt, Japan, or Korea, who faced greater cultural and linguistic differences.