The given sentence has been broken up into four different parts. The error, if any, will be in one or more parts of the sentence. Select the option which contains the part of the sentence which is free from an error. If all are incorrect mark Option 4 as your answer.

The killing of civilians in an allege use of chemical weapons (A) / by the Syrian government, has led to the build of (B) / momentum to begin another around of military strikes against the (C) / Bashar al-Assad-led government by the United States (US) and its allies.(D)