Caesar cipher

The transformation can be represented by aligning two alphabets;
the cipher alphabet is the plain alphabet rotated left or right by some number of positions.

For instance, here is a Caesar cipher using a right rotation of three places
(the shift parameter, here 3, is used as the key):

Plain:  abcdefghijklmnopqrstuvwxyz
Cipher: DEFGHIJKLMNOPQRSTUVWXYZABC

To encipher a message, simply look up each letter of the message in the "plain" line
and write down the corresponding letter in the "cipher" line. To decipher, do the reverse.

 Plaintext: the quick brown fox jumps over the lazy dog
Ciphertext: WKH TXLFN EURZQ IRA MXPSV RYHU WKH ODCB GRJ


Normally the spaces in between words would be omitted, however I am a nice guy.

Find the key, and procede to find Plaintext.

1)
Ciphertext:     FBTZ

2)
Ciphertext:     FVB ZVSCLK JHLZHY

3)
Ciphertext:     JRYPBZR GB PELCGBTENZF

4)
Ciphertext:     YMJ MFWIJXY YMNSL NS YMJ BTWQI YT ZSIJWXYFSI NX YMJ NSHTRJ YFC  FQGJWY JNSXYNJS

5)
Ciphertext:     R SZCCZFE YVIV R SZCCZFE KYVIV GIVKKP JFFE ZK RUUJ LG KF IVRC DFEVP  JVERKFI VMVIVKK UZIBJVE