As you know, there are a few formalities to be _____ before you enter a foreign country.

A．gone through

B．gone against

C．gone over

D．gone up

合成油的主要优点表现为在低温状况下，合成油具有较好的（）；在温度升高时，可以较好地抑制（）降低；高温时化学稳定性较好．可减少油泥凝结物和残碳的产生。