Step 1: Check statement (A).
Particle size and shape control how a grain or seed behaves in an air stream and against a screen aperture, since drag force and the ability to pass through a slot both depend on size and shape. This is a genuine design input, so (A) is correct.
Step 2: Check statement (B).
A cleaner has to be set for the actual mixture of good grain, broken kernels, chaff and dust in the lot being cleaned. Knowing how much of each fraction is present decides the screen sizes and air velocity to use, so the distribution of fraction sizes is a real design factor, making (B) correct.
Step 3: Check statements (C) and (D).
Sticky or abrasive material clogs screens and wears out blower and screen surfaces faster, so the designer must pick materials and clearances accordingly, confirming (C). Flow characteristics decide hopper slope, feed rate and vibration needed to keep material moving evenly through the machine, confirming (D).
Step 4: Combine the findings.
All four listed factors, particle size and shape, fraction distribution, stickiness and abrasiveness, and flow characteristics, are genuinely used while designing an air screen cleaner, so none can be dropped from the list.
\[ \boxed{(A), (B), (C) and (D).} \]