Spacecraft have been seen hovering over the White House over the last few weeks.
Step-by-step explanation:
Has is used with singular noun.
Have is used with plural noun.
The term “have” and “has” are used with the pronouns-plural noun and singular noun respectively.
Has is used in the sentence with present tense and present perfect tense.
Have is used in the present tense when the subject is a plural noun or the pronouns.
In the given sentence, spacecraft have been seen hovering over the White House over the last few weeks.