What does a group of pictures (GOP) start with?

What does a group of pictures (GOP) start with?

a) A GOP starts with an I-picture and ends with the last picture before the next I-picture.

b) A picture sequence which can be coded as an entity. For instance, it is possible to cut between GOPs. For that reason, the first picture in a GOP has to be intra-coded (I-picture). Time codes are carried on GOP levels.