3 sentences

1. 他背着我坐着，我看不见他的脸。

   tā bèi​zhe wǒ zuò zhe, wǒ kàn bù jiàn tā de liǎn.

   He is sitting with his back to me, so I can't see his face.

   Source: Dong Chinese Dictionary

2. 他背着父母偷偷卖掉了旧相机。

   tā bèi​zhe fù​mǔ tōu​tōu mài​diào le jiù xiàng​jī.

   He secretly sold his old camera behind his parents' backs.

   Source: Dong Chinese Dictionary

3. 为了拍摄日出，他背着沉重的相机包爬上了山顶。

   wèi​le pāi​shè rì​chū, tā bēi​zhe chén​zhòng de xiàng​jī bāo pá​shàng le shān​dǐng.

   To photograph the sunrise, he climbed to the top of the mountain carrying a heavy camera bag.

   Source: Dong Chinese Dictionary