未知题型 Conveying machinery refers to the transport machinery that continuously or intermittently transports bulk goods or finished goods according to the specified line.

单项选择题 子宫脱垂伴有尿道膨出会出现下列哪种症状

问答题 发育毒性是指出生前经父体或（和）母体接触外源性理化因素，引起在子代到达成体之前这段时间内出现的有害作用。试根据所学知识阐述发育毒性共有哪几个阶段，各阶段有什么特点？