REGULAR

1.geology

2.geometry

3.geography

4.geologist

5.action

6.enact

7.transport

8.import

9.portable

10.bicycle

11.cyclone

12.encyclopedia

13.autograph

14.automobile

15.automatic

16.autobiography

17.telegraph

18.photograph

         CHALLENGE

1.binocular

2.bicentennial

3.bilingual

4.bipedal

5.triceps

6.triathlon

7.traid

8.triplicate

9.unicorn

10.unify

11.union

12.unique

13.semicircle

14.semicolon

15.semiannual

16.centipede

17.century

18.centrnnial