I'm sure others have clearer answers but since I'm working through this myself now I'll have a crack.
Not d) - you'll be back in or nearly in cloud
While b) & c) might be what you end up doing they are limiting. You might have a reason (low cloud) not to want to use a particular side. Even if you might end up doing one of them you are actually doing a). as per allowed circling procedures. With cloud at 1000 you won't be doing a std. height cct in any case.

ENR 1.1-77 10.11.2 refers and gives you options not to follow std cct

The approach chart for RWY 22 at Hay has changed since that question was written. The point of the original question was that you are below the circling minimum at night and you can't land straight in. Your only choice is to do a missed approach. The question has been updated to reflect that.

Hi bob
the question has been mentioned before in 2014 in your forum

You are conducting an RNAV GNSS at night on RWY 22 at Hay, you break out of cloud at 990feet with a vis of 2,5km. If you are now too high to land straight ahead on rwy 22 you should?
a) carry out missed app.
b) continue to circling area overfly for lh circuit rwy 22
c) continue to circling area overfly for rh circuit rwy 22
d) climb back to 100 feet and fly a left circuit rwy 22.

You answer states that you are below MDA for circling which is 1000feet and can't be sure of 300ft terrain clearance...
But i have the box shaded grey and Hay has an AWIS (as listed in ERSA).
Wouldn't that now be an MDA reduced by 100 feet to 900 feet, allowing B to be the correct answer?

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And this was your explanation
This question refers to a RNAV GNSS approach into Hay. The QNH is not available - no ATIS or AWIS. The circling minimum is 1000 and you break out at 950 feet at night so you have to do a missed approach.

Because my book was revised that break out at 1000' and Hay has AWIS by phone, while Hay's Circling MDA remain the same which is 1000'(could become 900' due to shaded grey), I think my question has been updated already. So in this case circling approach is acceptable, I just don't understand what are wrong with b, c and d.

I think you will find that you don't have the visibility required for a straight-in approach anyway.

I have just bought IREX E-Text and set 8 Q 9 is showing that

You are conducting an RNAV GNSS at night on RWY 22 at Hay, you break out of cloud at 850 feet with a vis of 2.5km. If you are now too high to land straight ahead on rwy 22 you should?
a) carry out a circling approach.
b) continue to circling area and over fly for a left circuit rwy 22
c) continue to circling area and over fly for a right circuit rwy 22
d) climb back to 1000 feet and fly a left circuit rwy 22.

So just let you know a) in E-Text should be corrected 🙂