Evaluate the similarity between them and classify them into classes from 0-5 as follows:
0 : The two sentences are completely dissimilar.
1 : The two sentences are not equivalent, but are on the same topic.
2 : The two sentences are not equivalent, but share some details.
3 : The two sentences are roughly equivalent, but some important information differs/missing.
4 : The two sentences are mostly equivalent, but some unimportant details differ.
5 : The two sentences are completely equivalent, as they mean the same thing.

Let me give you an example: Sentence 1: A plane is taking off. Sentence 2: An air plane is taking off.
The answer to this example can be: 5
Here is why: Here both statements are talking about the same thing hence it will be classified as a 5.

OK. solve this:
Sentence 1: Close up of a white sheep with a black head. Sentence 2: A close-up of a sheep with a black head.
Answer:
4