Even though this question does not have options, it can be answered easily.
Answer:
The best method to combine the sentences is by adding a comma between them:
When a set of fingerprints is sent to a crime laboratory for identification, the general pattern of prints is verified first.
Explanation:
Sentence 7 is a subordinate clause, which is made clear by the fact it begins with the conjunction "when" and the fact that, on its own, it does not express a full thought. However, once we read it with sentence 8, we realize they complement each other. Sentence 8 functions as a main clause, making the thought expressed in sentence 7 complete. The best way to join the two sentences is by adding a comma between them. There is no need to alter anything else, since the appropriate conjunction is already in use.
