11. a range of 广泛的
She created a range of广泛的 sculptures in different styles in the 1940’s.

12. a rare treat
M: This casserole砂锅菜 really tastes good. I guess that’s because the vegetables in it are fresh instead of canned.
M: I know. Kind of a rare treat in this cafeteria.

13. a rule of thumb
A useful principle having wide application but not intended to be strictly accurate or reliable in every situation.
This basic chemical knowledge, which was applied in most cases as a rule of thumb, was nevertheless dependent on previous experiment.

14. a scorcher
a hot day
Hew! It’s a real scorcher today.

15. a selection of
The jewelry store doesn’t have a good selection of watches.

16. a series of
Reversals of the field give rise to a series of magnetic stripes条纹地带 running parallel to the axis轴 of the rift裂口.
A number of objects or events arranged or coming one after the other in succession.

17. a suite of
Their fossilization required a suite (套) of factors.

18. a torrent of
大量的
They brought a torrent of criticism on the experimenter.

19. a trace of
一丝
Scientists believe that when the oceans were young they contained only a trace of salt and their level of salinity含盐量has been growing gradually.

20. a variety of
各种各样的
We organize tours to a variety of places nearly every weekend.