Have* this is because has* is past tense and have is more appropriate since there are multiple things you are referring too (Mercury, Venus, Earth and Mars). To be honest, these planets have a molten core.
Inarticulate means not being able to speak or express clearly. In this case, Peter was inarticulate because he was angry when Mr. Dussel teases Peter about his cat which he loves very much. Not the same with Mr. Dussel who claims he is allergic to cats.
C, because fiction writing is typically not based on anything true
c. persuade the commissioners to place street lamps along the road
