the party will be held at 7 p.m.这里的WILL后面为什么要加BE呢?

晚会嘛,当然是是被举行的,所以这里要用被动语态哦.
被动语态的结构就是be+动词的过去分词啊,hold过去分词就是held了.
这里的be随时态变化,将来时,will后面加动词的原形（其他地方变形只变be即可）,所以用be.
至于举例子嘛：
1 party is being held now 晚会正在进行
2 party has been held 晚会已经进行了（可能还在进行中）
3 party had been held 晚会已经进行过了（已经结束了）
4 party was held at 7 p.m.晚会于7点钟开始进行（已经开始）
5 party was being held at 7 p.m.7点钟时晚会正在进行（现在已经过了七点）