Question

There were five original Iroquois Nations. In the early 1700s, the Tuscarora joined the Confederacy as the sixth.

Answer 1

b) There were five original Iroquois Nations; in the early 1700s, the Tuscarora joined the Confederacy as the sixth.

Of the four possible responses, there isn’t really a “best” way.  There is only one correct way to combine the sentences.  Option A is incorrect because this option contains a comma splice.  Option C is incorrect because it is run-on sentence.  Option D is incorrect because it contains a comma splice and an incorrectly used semicolon.  The thing to keep in mind with regard to periods and semicolons is that they are used essentially in the same manner when placed between two sentences.  A good rule of thumb to help yourself remember is that semicolons and periods are interchangeable, and if you cannot use a period, then you cannot use a semicolon.  Note, thus, that for Option B the period was simply replaced with the semicolon, which is absolutely correct.  (Of course, the “in” would need to be lowercased because only proper nouns should be capitalized if not beginning a sentence.)

Answer 2

The answer is B.  There are two clauses in this sentence, and each one of them has a complete thought, making possible for both phrases to stand on their own, not depending on each other. These are independent clauses that are joined  by a semicolon, and together they form a compound sentence. Another way to join them is by using a coordenating conjunction and a comma.