now and then与now and again 、once in a while

now

and

then

时而,不时（置于句尾）

e.g.

He

went

to

see

his

grandmother

every

now

and

then.

他时而去看看他的祖母。

now

and

again

时而

e.g.

He

chops

in

now

and

again.

他不时插一两句话。

once

in

a

while

偶尔,有时(置于句尾）

e.g.

He

comes

to

see

me

once

in

a

while.

他现在是偶尔来看看我。