Question

1._______,we should be glad. a、They arrive tomorrow b、Were they arriving tomorrow c、They were to

Answer 1

选C吧。你的C项应该为They were to arrive tomorrow .这应该是一个虚拟语句。是对将来的虚拟。
对将来的虚拟有以下几种用法
I.f +主语+should do ,主语+would do
2.If +主语+were to do ,主语+would do
3.If +主语+过去式,主语+would do
此题属于第三种，意思为他们要是明天能来，我们会高兴。

Answer 2

选B，should be 作为情态动词，可以用来表示有较大可能实现的猜测、推论。而明天到达还没发生，是将要发生，所以选B

Answer 3

选B

Answer 4

选C