Is 50% artery blockage more dangerous than a 90% blockage

I have read this on few sites that 50% is more dangerous than a 90%. Why is this so?
Also, is stent the only option to remove a blockage? Please help.

No, the more occluded the artery, the higher the risk of angina and myocardial infarction. There are other options, but a stent is the most commonly used and studied method, making it first line treatment.