p, m. b, n, w                             1 year                          -                       3 years

h                                              1 year                          -                       4 years

k, g, d                                      2 years                        -                       4 years

t, ng                                         2 years                        -                       6 years

f, y                                           2.5 years                     -                       4 years

r , l                                           3 years                        -                       6 years

s                                               3 years                        -                       8 years

ch, sh                                       3.5 years                     -                       7 years

z                                               3.5 years                     -                       8 years

j                                               4 years                        -                       7 years

v                                              4 years                        -                       8 years

th                                             4.5 years                     -                       7 years

zh                                             6 years                        -                       8 years