Verb conjugation of "zerren" in German

It would be an advantage if you could send it via DHL, UPS or another Currier, because the parcel was lost once when we sent it with regular mail. Please send me a reference number after you send it.
You have to be careful when you go on summer vacation. There are many dangers but the most dangerous one is the sun itself, because if you're not careful it may harm you. People underestimate the rays.
How do you like comics? I have actually never read them, but for learning a new language it is a great way; but the language often is not too correct. But it has mostly more advantages than drawbacks.