Directions: Choose the best answer from the four choices marked A, B, C and D.The mountains form a natural _________between the two countries.
A. prevention
B. obstruction
C. barrier
D. jam
They built a ten-foot high fence to _________the house against intruders.
A. assure
B. secure
C. insure
D. issue
Managers have learned to grapple with _________, artificial intelligence, computer-aided engineering and manufacturing.
A. joining
B. junction
C. networking
D. linking
One of the biggest _________advantages of the Internet is lower transaction costs.
A. abnormal
B. commercial
C. moderate
D. complicated