Nilesh, thanks for posting this.

for Q24:

i find the comments below too comlex.

here is an easier one:

honestly, somehow, Q24 only took me like 10secs, i went down the choices and circled D immediately.

here is my analysis: the lines goes [pharmacologist design drugs to specific receptors on defined categories of neurons],

so, why do they need "defined" ions? cuz it take the drugs to the specific receptors right?

so, the defined ions THEMSELVES MUST be somehow "special" or "specific".

its like, you wanna go to a place,a museum, you google it, and the answer may be that [you can take METRO1], but CANNOT be that [you can take public transportation], cuz this tells you nothing.

Hope it helps~