我是D类scientific research签证。你回来时只要签证部过期,理论上没问题。
Exemptions
You won’t need a visa if you:
are travelling to Australia, Canada, New Zealand or the USA and have a valid visa for that country
are travelling from Australia, Canada, New Zealand or the USA and it’s less than 6 months since you last entered that country with a valid entry visa
have a valid US permanent residence card issued on or after 21 April 1998 (or an I-797 extension letter issued by the Bureau of Citizenship if it’s expired)
have a valid Canadian permanent resident card issued on or after 28 June 2002
have a valid uniform format category D visa for entry to a state in the European Economic Area (EEA)
have a valid uniform format residence permit issued by an EEA state