The largest unknown area is the UK's future in the customs union, which provides for the frictionless movement of goods across Europe.
最大的悬念是英国在欧洲关税同盟的未来，后者使得商品可以在欧洲境内畅通无阻地流通。
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You can find lots of things you don't know when you make a plan, such as, the origin of a certain area, the customs of different areas, local food and so on.