Is - two billion dollars is a unit, one unit so it is singular and you use the singular verb
think - scientists is a plural, therefore, you must use the plural verb form of think
My thesis/topic sentence is true because <span>B facts</span>
8. b. comparison
9. b. comparison and/or contrast
10. d. time order
11. c. on vacation
12. b. there might be no yellow handkerchief on the tree
13. true
