Problems with Arduino on Mac

hey, i can't communicate with my arduino on my mac.

i have Yosemite, newest software version of arduino and arduino uno R3.There is no choosing option for arduino uno in the board menu

can you help me?

You already have it chosen: "Arduino/Genuino Uno".

i got sync errors between the mac and arduino

Sync errors means that the responses from the bootloader are not as expected. What, exactly, do the RX and TX LEDs on the Arduino do when you try an upload?