The sentence "I'm going to tell you something very important, so please _____ from... a heart attack." requires an appropriate adverb. An adverb that could fit in the blank to make the sentence meaningful is "listen." Therefore, the completed sentence would read: "I'm going to tell you something very important, so please listen from... a heart attack."
For the sentence "The old man died _______ a heart attack." the correct preposition to use in the blank would be "from." Therefore, the completed sentence would read: "The old man died from a heart attack."
In the sentence "More than one person _______ going to have to find a new job," the correct verb to use in the blank would be "is." Therefore, the completed sentence would read: "More than one person is going to have to find a new job."
In the sentence "You'll _______ tell the police that your house was broken into," the correct modal verb to use would be "have to." Therefore, the completed sentence would read: "You'll have to tell the police that your house was broken into."