Create a function that replaces "the" in the sentence with "an" or "a". Remember that if the next word begins with a vowel, use "an". In the case of a consonant, use "a".
replace_the("the dog and the envelope") ➞ "a dog and an envelope"
replace_the("the boy ran at the wall") ➞ "a boy ran at a wall"
replace_the("the egg, the spoon and the espionage") ➞ "an egg, a spoon and an espionage"