Which is a sentence fragment?

a.
although they sang well.

b.
he chuckled to himself.

c.
fresh water bubbled up from the spring.

d.
on the train, conductors collected tickets

What chapter explain.

To form soil, the two processes which must occur are erosion and weathering, so the correct answer is "soil formation is a continuous presses, but also one which takes a long time, it can sometimes take more than five hundred years for 1cm of soil to form.

  i think it is   b because it to subject