Answer:
B. Please get out the flour and sugar, and I'll find the mixer.
C. After Will makes a prediction, we can start the science experiment.
D. Fortunately, the weather will be perfect for a hike.
Step-by-step explanation:
A. contains a comma splice.
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FYI:
To avoid the redundancy, you needn't say "Choose all that apply" because the verb 'are' signals that there is more than one correct answer.
If there were only ONE correct answer, the question would read:
"Which of the following sentences IS punctuated correctly?