What tool would a government most likely use to restict imports based on health and safety concerns?

Bonus question: according to wikipedia, in chinese philosophy yin and yang "describes how seemingly opposite or contrary forces may actually be complementary, interconnected, and interdependent." what are some examples from the story that amy tan may have intentionally incorporated elements of yin and yang philosophy into this story? select 2.

What makes water a renewable source

What was discussed at the yalta conference