Is there a sentence fragment?
On November 3, 1957, the Soviet Union sent the first animal into space—a dog named Laika. Which had been found as a stray living on the streets of Moscow.
A: no
B: yes
There is a sentence fragment that does not express a complete thought.
On November 3, 1957, the Soviet Union sent the first animal into space—a dog named Laika. Which had been found as a stray living on the streets of Moscow.
Here is one way to fix the sentence fragment:
On November 3, 1957, the Soviet Union sent the first animal into space—a dog named Laika, which had been found as a stray living on the streets of Moscow.