How nice the weather is! ?

1. The first one is an exclamatory sentence.

Formula: What?

A/An

adjective

Countable noun

subject

predicate

what

adjective

uncountable noun

subject

predicate

The weather is incalculable, so set Formula 2.

2. Must

be

do

Speculation about current facts

must

have

Disappearing means positive speculation about past facts.

should

have

Done means that you should do something, but you didn't actually do it.

The telephone was invented before the car.

Common sense problem

Use prepositions in a specific year.

4.the

Rest means rest, in the plural.

this

rest

About ... also means rest.

The singular and plural of its predicate verb depends on the singular and plural of the noun behind it.