these are book and ruler 里面里的book和ruler 需要加s吗

前面的book一定要加s,因为谓语是are,主谓一致就近原则,谓语are就主语books近,所以要在book的前面加s。如果后面的ruler没有冠词a的话也要加s,加了冠词a的话变成these are books and a ruler。就不用加s了。