Material Mix and Yield Variance

The following question is from BPP Mock Exam 1.
The following cost information relates to product XY, which is produced in a continuous process from several different materials.
…………………………………………………………………………………………………….$
Actual quantity of materials at standard price………………………………..19960
Actual quantity of materials at actual price…………………………………….23120
Actual yield at standard materials cost………………………………………….20800
Standard yield from actual input of materials at standard cost………..19552

What is the materials yield variance for the period?
A) $ 1248(F)
B) $ 2320(A)
C) $ 840(F)
D) $ 3568(F)

This is their explanation and answer.
Correct Answer C

Standard yield from actual input of materials at standard cost ……….$19552
Actual yield at standard materials cost …………………………………………$20800

Mix Variance (195520 – 20800) : $1248(F). There are typing errors.

I know that “Standard yield from actual input of materials at standard cost” means “actual total input in standard mix at standard cost” but I don’t understand “Actual yield at standard materials cost ”
Does it mean “standard input in standard mix at standard cost” Please, help me.