Hardly/Scarcely/Barely had...done...when...;No sooner had...
Hardly/Scarcely/Barely had...done...when...;No sooner had...done...than...
Hardly/Scarcely/Barely had...done...when...;No sooner had...done...than.when和than从句里为什么用一般过去时?这两句的连词,为什么一个是when一个是than