Yes, there is an option where you can X out answers. I'd suggest taking one or two practice tests within the LSAC's lawhub environment (you should have access to it) -- this is the exact same testing environment/setup you'll see on test day. This way, you'll get used to where all the buttons are and the slightly different font/spacing on the test.

Hi, I've had similar issues, where I thought the 70s were not that bad and then getting destroyed by the 80s. One thing I've noticed is that it a slightly different feel of a test (distribution of question types, etc, are slightly different, along with a "miscellaneous" game). For these, it's just to get used to the feeling of the 80s tests and drill these. It is very likely that the flex tests are going to be taken from the 80s era than the 70s era. Not sure if these comments helped -- happy to hear other's suggestions.

In the case of weaken questions, we are generally asked to attack the argument, and thereby we can't assume that all the premises are true. Even though directly attacking a premise almost never happens, indication that a premise may not be true is a strong weakening option. In this case, the premise states that: "All nations that place a high tax on income thereby produce a negative incentive for technological innovation" that is to say, that all nations that limit the extent to which people can make money have an effect on technological innovation. Answer choice B directly contradicts this, and therefore this argument fails, weakening it.