1 to have to

2 must

3 compulsory

4 necessarily

1 there is no need

2 why should

1 to pervade

2 to fill the air

3 diffuse

4 everywhere present

5 about to inundate (water)

6 permeated by (smoke)

7 filled with (dust)

8 to saturate (the air with fog, smoke etc)

1 to complement

2 to make up for a deficiency

1 need not

2 not obliged to

3 not necessarily

1 a pack of lies (idiom)

1 trying to hide it makes it more conspicuous (idiom); A cover up only makes matters worse.

1 to become more resolute with the passing of time (idiom)

1 Although the peony is beautiful, it depends entirely on help from the green leaves (idiom). However brilliant you may be, you can't do anything without support from others.

1 lit. whoever hung the bell on the tiger's neck must untie it (idiom)

2 fig. whoever started the trouble should end it