Which sentence does not have an error in subject and verb agreement?
a. glimmering sun and crashing surf has a soothing effect on me.
b. isn't basil and thyme two herbs you use in your sauce?
c. a piece of cake with a candle was brought to my table on my birthday.
d. the curtains, soft and white, was billowing in the breeze.

From the options indicated above, the sentence which has correct subject and verb agreement is:

C.A piece of cake with a candle was brought to my table on my birthday.

The subject "piece of cake" takes a simple singular past tense of the verb "was" and all the other parts of the sentence are in accordance to its correct grammatical patterns.

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.