Step 1: Check the indented cylinder separator.
This machine is a rotating cylinder with shallow pockets on its inner surface, particles shorter than the pocket depth get lifted out and fall into a collecting trough while longer particles slide back down, this is the classic length-based separator, so it qualifies.
Step 2: Check the disc (disk) separator.
A disc separator uses several rotating discs, each carrying indented pockets on its rim, working on the same lifting principle as the indented cylinder, only shorter particles are retained in the pockets long enough to be lifted and discharged. Functionally this is also a length grader, so it qualifies too.
Step 3: Check the inclined draper and rotary screen cleaner.
An inclined draper is simply a moving canvas or belt apron used to carry cut crop sideways on a harvesting platform, it does not sort particles by any dimension. A rotary (reel) screen cleaner passes material through round or slotted perforations and therefore grades by width or thickness, not by length. Neither belongs in a length-separation list.
Step 4: Conclude.
Only the indented cylinder separator and the disc separator genuinely separate material based on length, giving (A) and (C) only.
\[ \boxed{(A) and (C) only.} \]