Participants can use any external sources. ClueWeb12 is an example of text collection that can be used to support creating answers for our subtasks:
ClueWeb12 ( http://lemurproject.org/clueweb12/)
Please note that: An agreement with or obeying the License from the 3rd party are required. For example, the corpus ClueWeb12 requires an agreement between participants and the 3rd party Carnegie Mellon University (cf. http://lemurproject.org/clueweb12/index.php#Obtaining).