Question

sls: printer characteristics
use the information below to answer the question.
layer height
the layer height selected for sls is typically 0.1 millimeters thick. this is the same height used by desktop fused filament fabrication machines when printing parts on the highest resolution setting.
powder size
the other aspect that affects the surface quality of printed parts is the size of the powder. finer powder particles will create parts with a higher resolution and better surface quality. however, issues may occur with the spreading mechanism used during the re - coating. a coarser material could have a detrimental effect on the surface finish.
bin size
when planning an sls print, bin size and packing is an important consideration. the efficiency of the build will depend on the orientation of the forms and how well they are placed within the bin. each bin has a fixed size. however, the total print time will be determined by the height of your build. the print cycle will take the same length of time regardless of the number of items being created in the batch
what can have a detrimental effect on the surface finish of an sls print?
a polymer powder
a drier material
a thermoplastic powder
a coarser material

Explanation:

In the "Powder Size" section, it's stated that finer powder gives better surface quality, and a coarser material (opposite of finer) could have a detrimental effect on the surface finish. The other options (polymer powder, drier material, thermoplastic powder) don't relate to the factor affecting surface finish as per the given info.

Answer:

a coarser material