For 10 points, name this 18th letter of the English alphabet.
"Herbert and Eve Clark found that even though young children frequently made the sound represented by this letter while babbling, it was one of the last they learned in actual speech. In American English, only a lax vowel may precede this letter's sound if they are in a single syllable. Some accents prevent back-to-back vowel sounds in two syllables by inserting an "intrusive" kind of this letter in between them. This letter represents a range of sounds, but the most common is a postalveolar approximant. Lateral consonants and the sounds produced by this letter make up the class of (*) liquid consonants. The back of the tongue may be bunched or the vocal tract may be constricted in a process by which a vowel is "colored" by this letter. Most accents in England drop this letter's sound when it is not followed by a vowel, making them non-rhotic. For 10 points, name this 18th letter of the English alphabet.
"Herbert and Eve Clark found that even though young children frequently made the sound represented by this letter while babbling, it was one of the last they learned in actual speech.
R [prompt on “rhotic consonant”] &lt;Bailey&gt;