Re: how/how much
1a and 1c are reasonable interpretations. 1a must be true in order for 1c to be true. It is possible to interpret "how" as "how much" - some decades ago, you might have heard "Oh, how he has changed" and it would mean "Goodness me, he has changed a lot". However, this usage is not as common these days.
Originally Posted by navi tasan
Your second example sentence is not very natural so it is difficult to say how it would be interpreted. I would expect to see "I have noticed how alike they are", which would mean both 2a and 2b. 2c would really only be worded as you have worded it in 2c.
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