Which of the following characteristics apply to the soliloquy speech form? select all that apply.

reveals a character's inner thoughts
like the aside, is not heard by the other characters
usually spoken when others are on the stage
allow actors flexibility in interpretation

The characteristics that apply to the soliloquy speech form are the following:
reveals a character's inner thoughts - this one is for sure, given that the character is speaking out loud what they are thinking at the moment
As for the second one, I'd choose the second option - like the aside, is not heard by the other characters, given that other characters can be present, but the soliloquy is not told to them. 
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