Multiple wh-interrogatives are questions with two non-identical wh-signs; thus, they ask for pair list answers. In LSC, there is a preference to move just one of the two wh-signs towards the end of the clause, leaving the other in situ.
a) wh-object moved + wh-subject not moved
wh
who buy what
‘Who bought what?’
b) wh-subject moved + wh-object not moved
wh
what buy who
‘Who bought what?’
(examples a-b based on Alba, 2016: 102)
Although both wh-signs can be located at the end of the sentence, this is dispreferred. Moreover, it is not possible to locate both wh-signs at the front of the clause.
wh
a) buy who what
‘Who bought what?’
wh
b) buy what who
‘Who bought what?’
(examples a-b based on Alba, 2016: 102)
If both wh-signs are located at the end of the clause, LSC prefers to leave the wh-object in a more peripheral position, preceded by the wh-subject. Example (a) right above, then, is preferred by LSC signers.