Hétóng yǐjīng dàoshǒule, nà jiù chūqù qìngzhù yīxià ba. The contract is in the bag, so let's go out and celebrate.
Tāmen hù bāng hùzhù, bǎ xiàoqìng gǎo dé hěn chénggōng. They helped one another to make the school festival a success.
Wǒ méi qǐng tā lái cānjiā qìngzhù huì, gǎndào yǒudiǎn nèijiù. I feel a little guilty that I didn't invite him to join the celebration.