The correct answer is C) three months either way of the certificate's anniversary date. The reasoning is that according to the Load Line Convention, the annual survey for endorsement of a Load Line Certificate must be carried out within a three-month window, either before or after the certificate's anniversary date. This allows for some flexibility in scheduling the annual survey while still ensuring it is conducted on a regular basis. The other options are incorrect because they do not accurately reflect the three-month window requirement. Option A and B are too restrictive, while option D is too specific and does not account for the full three-month period on either side of the anniversary date.