<p><because their="" flight="" was="" missed,="" the="" bride's="" parents="" ran=""> frantically to another part of the airport to catch another plane that might still arrive in time for the wedding.</because></p>
<p>I chose</p>
<p><the bride's="" parents="" had="" missed="" their="" flight,="" then="" they="" ran=""> as the correction but the bb said its <because the="" bride's="" parents="" missed="" their="" flight,="" they="" had="" to="" run="">.</because></the></p>
<p>Isn't the second one changing the meaning and why is the first one wrong? Is it because "had" is unnecessary?</p>
<p>“Changes the meaning” is not a rule on the grammar section of the test. It just isn’t, no matter what people say.</p>
<p>The first one is wrong because of coordination rules. The word “then” produces a dependent clause, but when you have an independent clause first and a dependent clause second, you don’t use a comma. When you have DC followed by IC, you use a comma (like this sentence does, and the second option above).</p>
<p>The problem is much more serious then proposed above. “Then” is not a coordinating conjunction. Nor is the use of “then” above that of a subordinate conjunction. Simply the “then” above starts a new sentence. The comma must be replaced with a period or a semicolon.</p>
<p>There are six coordinating conjunctions in English – and, but, or, yet, for, nor, so.</p>
<p>Note the “then” can introduce a clause in a conditional sentence – i.e. “If … then …” but the sentence above is not of this type. The pair “if” “then” are correlative conjunctions.</p>