Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

[EX Q]: mariner 10 was a robotic nasa space probe.
[EX A]: mariner 10

[EX Q]: euclid's lemma, also called euclid's division lemma or euclid's first theorem, is an important lemma.
[EX A]: euclid's lemma

[EX Q]: halling railway station is a railway station in halling in kent.
[EX A]:
halling railway station