Received a PM for this one

To the original poster: this question is very confusingly transcribed. Unlike the Official Guide, which uses an em-dash (the big dashy looking thing) to separate the parenthetical phrase beginning '...they are often green', your question uses an em-dash (which you interpreted as a hyphen) to separate two independent clauses, a grammatical nicety that would lead straight to answer is (D). The answer was (B) however, and my head was spinning trying to figure out how that could be the case. Surely, joining a dependent clause to an independent clause is verboten. What I did not see was the hyphen hidden, without any intervening spaces, between bruises and heirlooms.
Only after I hunted down question #132 in the OG did I realize that the sentence was very different from the one transcribed here. There are two distinct em-dashes, as I've faithfully recapitulated below

:
Although appearing less appetizing than most of their round and red supermarket cousins, heirloom tomatoes, grown from seeds saved during the previous year--they are often green and striped, or have plenty of bumps and bruises--heirlooms are more flavorful and thus in increasing demand.
(A) Although appearing less appetizing than most of their round and red supermarket cousins, heirloom tomatoes, grown from seeds saved during the previous year
(B) Although heirloom tomatoes, grown from seeds saved during the previous year, appear less appetizing than most of their round and red supermarket cousins
(C) Although they appear less appetizing than most of their round and red supermarket cousins, heirloom tomatoes, grown from seeds saved during the pervious year
(D) Grown from seeds saved during the previous year, heirloom tomatoes appear less appetizing than most of their round and red supermarket cousins
(E) Heirloom tomatoes, grown from seeds saved during the previous year, although they appear less appetizing than most of their round and red supermarket cousins
Explanation:A good way to attack this question is to ignore the parenthetical phrase, "they are often green and striped...". Instead we need to focus on the two parts of the sentence, i.e. the part that comes before the first dash and the part that comes after the second dash. Notice the subordinating conjunction, 'although...' This suggests that the first clause needs to be a dependent clause that connects grammatically to the independent clause, "heirlooms are more flavorful..."
(A) Here is an attempt to make the underlined part a combination of a dependent clause ("Although appearing...") and an independent clauses ("heirloom tomatoes). However 'heirloom tomatoes' an independent clause does not make.
(B) "Although...appear less appetizing..." is a dependent clause. This matches up well with the independent clause following the second dash (the non-underlined part). The Answer.
(C) Same problem as (A).
(D) This answer choice forms an independent clause. Two independent clauses cannot be joined by a parenthetical comment (regardless of whether that comment is separated by em-dashes--as seen here--commas, or even parentheses). On the other hand, you can use just one em-dash to separate independent clauses (which is how I originally interpreted the question, and was thus drawn to (D)).
(E) Sounds awkward by placing 'heirloom tomatoes' before the although.
Hope that helps!