Knots in yarn

[DinahB]

I have knitted about 10 rows in a new project and have discovered that there are at least 3 knots where the yarn pieces were tied together. It looks terrible. I am fairly new to knitting, but have not had this happen so far. Do skeins of yarn often have lengths of yarn tied like this. Should I keep working or discard this? I am making a pair of slippers and can't imagine a knot of any kind would be comfortable.