Which sentence uses a verb that agrees with its subject?

a.
inside the velvet box sparkles two diamond rings.

b.
on the far side of the lake was some beaver dams.

c.
somewhere in these boxes is my birth certificate.

d.
after the winter and spring come the summer.

The correct answer is C.  Somewhere in these boxes is my birth certificate.

The corrections for the other answer choices are as follows:

A) Inside the velvet box sparkled two diamond rings.

B) On the far side of the lake were some beaver dams.

D) After the winter and spring came the summer.