Thanks for this! Regarding your comment on "Mandarin speakers have difficulty with many English consonants because sounds such as “th,” “r” and “l,” which are hard for Mandarin speakers, are pronounced with the tip of the tongue at the front of the mouth, and Mandarin is mostly pronounced with the back of the tongue at the back of the mouth.", I don't think it's right. In Mandarin, there are sounds like r, l, n, s, sh, c, chi, z and zh. To pronounce these, a speaker has to use his/her tip of the tongue at the front of the mouth. As I a Mandarin speaker, I think it hard to pronounce th, f, v. Thanks.