When a 3rd tone (low dipping level) appears before another 3rd tone, the first one changes to a 2nd tone.
1. 语法yǔfǎ, grammar
2. 雨伞yǔsǎn, umbrella
3. 保养bǎoyǎng, keep fit, maintenance
4. 洗脸xǐliǎn, wash face
5. 广场guǎngchǎng, square
6. 老鼠lǎoshǔ, mouse
7. 老虎lǎohǔ, tiger
8. 勇敢yǒnggǎn, brave
To learn more, you can visit:
http://learnchineseabc.com/chinese-pinyin-tones-sandhi-of-3rd-tone.htm