The correct answer is 1) immigrants should make every effort to adapt to their new country, including adopting cultural norms and traditions.
The statement that aligns most closely with assimilation is "immigrants should make every effort to adapt to their new country, including adopting cultural norms and traditions."
Understandably, immigrants love and respect their customs, religion, culture, and traditions. They can keep it. But for them to really integrate into the new country's society they have to make an effort to understand, respect and adapt to -in this case- the United States culture. That is the importance of assimilation, to accept an value the way in this country feels and thinks.