Here’s an easy way to find the main idea of a reading comprehension passage:
Look to the first or last sentence of the first paragraph, or the first sentence of the second paragraph. Chances are, the main idea/main argument of the passage will be in one of those places.
But beware! Often, the passage will discuss the opposing point of view somewhere in along the way to illustrate its main point (and trip up careless readers). So if you think you’ve identified the main point, take one final look at the context of the statement to make darn sure you’re not locked-on to the OPPOSITE view point that’s just being discussed as part of the argument.