1 . John had a great feeling of loneliness, ______ was even more serious during his lunch break.

A．which

B．it

C．what

D．that

2 . A year is divided into four seasons, as we all know, _______ the first is spring.

A．which

B．of them

C．when

D．of which

3 . His parents forced him to be a lawyer, ______ was against his own wishes.

A．when

B．which

C．that

D．what

4 . ________is reported, vaccines (疫苗) do an excellent job of preventing serious Covid-19 illness and deaths, but are less good at stopping infections, particularly since the emergence (出现) of the more infectious Delta variant.

A．It

B．Which

C．That

D．As

5 . Mother bought many tomatoes from the market two days ago, some of ______ have gone bad due to the hot weather.

A．those

B．which

C．whom

D．that

6 . Having a mix of male and female nurses also helps create a fun atmosphere, _________ helps patients recover faster.

A．this

B．that

C．which

D．where