What instrument was essential to the development of the cell theory?

The answer is: The Light Microscope

Explanation: there is no need for an explanation, i just got 100% on my test with this question and there was no normal Microscope it was a light MICROSCOPE.

it's d - life cycles - apex

you know that this symptom is misleading and quite often is related to: heart attack

a heart attack is a condition that occurs when the blood flow that transports oxygen to the heart muscle is damaged or cut off completely. the coronary arteries that supply the heart muscle with blood flow can be blocked by the accumulation of plaque. also, when the plaque within the heart artery breaks, it creates blood clot that can also hinder the blood flow. men that are over 45years of age and women that are over 55years of age are at risk of having a heart attack. the symptoms of a heart attack include chest discomfort, chest pain, coughing, and shortness of breath.