People still don’t know how languages get originated.（)

Many people know the importance of business ethics, but still some people don’t keep to it.（)

— How are you getting along with your study？ —___.A、Fine. What about you？B、I don’t know.

I don’t know the origin of this custom.

I don’t know the origin of this custom.

I don’t know the 【origin】 of this custom.A.nature

I don’t know the 【origin】 of this custom.A.nature