occur的解释：
v.发生;出现;存在;产生
第三人称单数： occurs
现在分词： occurring
过去式： occurred
过去分词： occurred
occur的用法例句：
1. If these drugs are stopped abruptly then some withdrawal symptoms mayoccur.
如果突然停服这些药，则可能出现一些戒断症状。
2. Keep a pad handy to jot down queries as they occur.
手边放一本便笺簿，以便有问题时随时记下。
3. Nitrates are chemicals that occur naturally in water and the soil.
硝酸盐是水和土壤中自然存在的化学物质。
4. Emergency cooling systems could fail and a reactor meltdown could occur.
紧急冷却系统有可能失灵，核反应堆有可能发生堆芯熔毁。
5. Unless you respect other people's religions, horrible mistakes and conflict willoccur.