There may be annexed to a district any of the following territory which is in the same county as the district, or in any other county:
a. Any territory contiguous to the district.
b. Any territory, any point of which touches the district.
c. Any territory separated from the district by a “separating barrier,” which term includes a street, road, highway, railway line, railway crossing, railway right-of-way, watercourse, lagoon, or other natural barrier.
d. Any territory specified in this section may consist of one or more separate parcels of land, but it is not necessary that all parcels shall constitute in the aggregate one tract of land.