<span>Le Morte d'Arthur is a reworking of existing tales by Sir Thomas Malory about the legendary King Arthur, Guinevere, Lancelot, Merlin, and the Knights of the Round Table. </span>
<u>Answer:</u>
Stop [!] the train is approaching.
<u>Explanation:</u>
The punctuation should be an exclamation point because it used at the end of a sentence or a short phrase which expresses very strong feeling.
<em>Hoped this helped.</em>

Apparently it's from the 15th Century's Old French emploier, Latin implicāre to entangle, to engage, from plicāre to fold
The subordinate clause is "when you go outside."
A subordinate clause contains a verb and a subject. Also, this type of clause doesn't form a complete sentence.
The subordinate conjunction is when, the subject is you, and the verb is go.