According to the passage, which of the following statements is TRUE

A．Linguists have found that sign languages and spoken languages differ from each other in many fea- tures.
B．Like spoken languages, which use units of form to produce words, sign languages use units of sounds.
C．Separately, b, e, and t have a meaning and together they form the word bet.
D．Spoken languages contain units of form that by themselves hold no meaning, but when combined create a wor