Tennis balls ______ best in summer. A) sell B) are on sell C) will be sold out

A.barrier property

B.thermal property

C.electrical property

D.mechanical property

(1)一堂数学课和一堂经济学课;

(2)网球和网球拍;

(3)牛排和龙虾;

(4)目的地相同的飞机旅行和火车旅行;

(5)熏肉和鸡蛋。

Which of the following combinations of goods are complements and which are substitutes？ Could they be either in different circumstances？ Discuss.

a. a mathematics class and an economics class

b. tennis balls and a tennis racket

c. : steak and lobster

d. a plane trip and a train trip to the same destination

e. ; bacon and eggs

A.Two black balls

B.Three black balls

C.Two red balls

D.Three red balls

Yangzhou pork balls is one of the popular dishes of()

A.Sichuan cuisine

B.Guangdong cuisine

C.Huaiyang cuisine

D.northern cuisine

A vessel servicing a pipeline during the day shall display ______.

A.three black shapes in a vertical line; the highest and lowest are balls，and the middle one is a diamond

B.three shapes in a vertical line; the highest and lowest are red balls，and the middle one is a white diamond

C.three black balls in a vertical line

D.two black balls in a vertical line

A. bitter

B. sour

C. sticky

D. spicy

A.in……on

B.in……under

C.to……under

D.toward……at

A vessel not under command shall display ______.

A.two red lights at night and two black balls during daylight

B.two red lights at night and three black balls during daylight

C.three red lights at night and two black balls during daylight

D.three red lights at night and three black balls during daylight

A.⑤①②④③

B.⑤②①④③

C.⑤④①②③

A.Two green balls in a vertical line

B.Two black balls in a vertical line

C.A black ball at the foretruck and yardarm ends

D.A shape of two cones point to point