Sentences 3 and 4: When the dress code demands a certain attire to be worn. But how do you know what to wear?
Which of the following options BEST\u00A0represents how the underlined\u00A0portion of these sentences should be written?

Sentences 3 and 4 are sentence fragments, which can be corrected by replacing the period with a comma and eliminating the word \u201CBut.\u201D When using a coordinating conjunction, such as \u201Cbut,\u201D the first part of your sentence needs to be an independent sentence. In this case, the first part of the sentence was not a complete thought; therefore, a coordinating conjunction (i.e. but, and, or) cannot be used to correct it.