Solution:

As shown ∠ BAC = 120.

After point C, it is the extension line from point D CD⊥BA to BA.

∵∠BAC= 120 ∴∠CAB=60

∵CD⊥BA？ ∴∠D=90？ ∴∠ACD=30

AC = 2？ ∴AD= 1,CD=√3

In RT△BCD, BD = 5 and CD = √ 3? ∴BC=2√7

∴sinb=cd/bc=√3/2√7=√2 1/ 14

Then the answer to this question is D(ps: I can't type the root sign, so I use √ instead of the root sign, please forgive me).