Which sentence contains a punctuation error?

a. we used one-half cup of chopped onions in the recipe.

b. it will be chilly later, so bring your blue-green sweater.

c. it is a well known fact that the earth revolves around the sun.

d. about one third of my friends have pet dogs.

Bicycle riding should be encouraged, and adding bicycle lanes will increase the number of riders. it is healthier for people to ride than to sit angrily in traffic. it is healthier for everyone to breathe cleaner air. sharing the road can be tricky, but there are things that can be done. so, add the bike lanes and get rolling! which sentence would improve this conclusion? every town should consider adding bicycle lanes, because it is a great idea. organizing safety classes for drivers and cyclists will ensure that everyone knows the rules. do not listen to negative people who complain about anything new. it is true that some people might get injured, but even walking can be dangerous.