81.   Six helicopters and an unmanned spy plane with a mounted camera were used to patrol the hilly terrain while Mandela was speaking.

82.   The hilly terrain in the centre of the country has made it hard to combat rebels.

a. + terrain >>共 390
rugged 9.79%
sloping 9.03%
mountainous 8.76%
rough 5.73%
higher 5.14%
difficult 4.49%
hilly 4.43%
rocky 2.38%
new 2.16%
steep 1.73%
hilly + n. >>共 98
terrain 22.97%
area 13.45%
region 6.44%
street 3.08%
country 2.80%
course 2.24%
stretch 1.96%
countryside 1.96%
capital 1.96%
outskirt 1.96%
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