This question has options. Answer the question about text:

Perhaps it came loose itself with use . I tightened it and got back to work . When I switched to my straight stitch machine , again I found the foot had been unscrewed and was loose . While I do occasionally need to switch feet on this machine , I had done no sewing the day before that would have forced me to unscrew the foot to switch it out .

What is the cause of my foot problem ?
Choices:
(a). It 's too old ..
(b). None of the above choices ..
(c). It 's not comfortable ..
(d). It 's too tight ..
(b).