2 sentences for 忽 (hū)

1. 天气忽冷忽热，让人难以适应。

   tiān​qì hū lěng hū rè, ràng rén nán​yǐ shì​yìng.

   The weather fluctuates between hot and cold, making it hard to adjust.

   Source: Dong Chinese Dictionary

2. 由于他的疏忽，原本万无一失的计划最终出了岔子。

   yóu​yú tā de shū hū, yuán​běn wàn​wú​yī​shī de jì​huà zuì​zhōng chū le chà​zi.

   Due to his negligence, the plan that was supposed to be foolproof ended up hitting a snag.

   Source: Dong Chinese Dictionary