Read the following context and choose the best option to answer the question.
Context: 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 .
Question: What is the cause of my foot problem ?
Options: 
- It 's too old .
 - None of the above choices .
 - It 's not comfortable .
 - It 's too tight .


None of the above choices .