Hannah just finished building a house of cards that stands four stories high. she is worried that it will fall down. which of the following statements must be true? a. a house of cards is too fragile and must fall down eventually due to gravity. b. if hannah adds another card to the house of cards, then it will fall down. c. as long as nobody touches the house of cards, it will remain standing. d. if no unbalanced force acts upon the house of cards, then it will remain standing forever.

the answer is if no unbalanced force acts upon the house of cards then it will remain standing forever.

explanation:Newton's first law of motion states that an object at rest will remain at rest unless acted upon by an unbalanced force.  

Even if nobody touches the house of cards, another type of unbalanced force (like wind) could knock the cards down, or if Hannah adds another card to the house of cards, it may or may not fall down.

However, if no unbalanced force acts upon the house of cards, then it will remain standing forever.

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