Write the next sentence in this paragraph:

How to open train doors
Check for buttons or handles on or near the doors.
Some trains will have buttons or handles that let you open and close the doors. On other trains, the operator may be the one who controls when the doors open and close.

Available choices:
a). Check to see if there are handles or open and close buttons on or next to the train doors. These buttons will generally indicate their function with text on or near the button such as " press to open, " or " open " and " close.
b). Check to see if the doors in the train have decals on them. Decals or decals will indicate how many doors there are in the train.
c). If you're having trouble discovering which door knobs or handles the passengers have access to, inspect any signs on the doors to make sure that they do not come into contact with anyone. Some doors may be labeled with numbers that start with " 1 " or a combination of the four numbers.
d). Look for these buttons at specific train entrances. Some train doors may not start as a chat device, but they may also have knobs on the bottom of the door.
a).