task fmri preprocess and first level

Hi. Professor Yan

I got two questionas about task fmri data preprocess and first level analysis.

1 There was two kinds of task with four runs for my data. In the preprocessing, should I preprocess the data one run by one run, or one task (two runs) by one task, or four runs together?

2 For the first level analysis, is it necessary to add WM and CSF signal as covariates？ If so,  how do I get WM and CSF signal in the preprocessing?

Look forward to your reply.

Best

Bekcy