Answer:
B, "is situated"
Explanation:
Process of elimination:
A: The Oval Office is in the White House today, so the sentence should not be in the past tense.
C: This is not grammatically correct. The sentence needs a verb of a tense of "to be" like "is" or "was".
D: This is not grammatically correct. The sentence needs a verb of a tense of "to be" like "is" or "was". Also, since the Oval Office is singular, the word would be situates instead of situate anyway.
