Answer:
B.) Because.
Step-by-step explanation:
Plug in the words.
A.) Consequently.
The frosting itself was perfect; it only became runny consequently it was so hot outside.
This sentence doesn't make sense.
B.) Because.
The frosting itself was perfect; it only became runny because it was so hot outside.
This sentence makes sense.
C.) During.
The frosting itself was perfect; it only became runny during it was so hot outside.
This sentence doesn't make sense.
D.) Even though.
The frosting itself was perfect; it only became runny even though it was so hot outside.
This sentence doesn't make sense.
Therefore, your answer is B.)
Hope this helped, have a good day! <3