I'll translate the answers in the strategy book.
There is actually two explanation for question 2, one from the author of the book, and one from the editor, (you may know him) fukuchi.
Author: by throwing the
( 
edit
) tile you can leave two very strong shapes leftover to get a good tenpai wait (talking about the 1234567s and 4567m) and by throwing the
(dama) you lose any change in wait using the souzu but instead you get a good wait by drawing either the
or
tile. However in this particular circumstance, by drawing the
(itssu potential as well) and
, you get a 3 sided wait and therefore I have decided that not taking tenpai is more advantageous in this case. if the souzu was in the shape of
,
(dama) is instead more advantageous.(due to lack of three sided waits potential)
Fukuchi: an oya who is down in points should just riichi whatever the wait but in this case the hand is too good, a hand that can be a game changer. Being so early on, the answer should be
to maximise the possibility of wait being at least double sided. In actual game play, I will likely throw the
but ideally you want to be able to throw
every time
My Comment I actually personally chose
(dama) and just as a reference, they did a questionnaire and for this question only 38% of people got it right (out of like 58 established? mahjong players) but I definitely understand where they are coming from. Not taking tenpai early on to maximise the possibility of a good wait is not rare and usually considered the more correct choice in particular circumstances. The question is, is this case that particular circumstance, and it is definitely close between
(dama) and
( edit
).
(riichi) is however generally considered not too good if it's still early on
EDIT I acually noticed a mistake in one of the questions, slight one, don't know if you would have changed you answer but the manzu should actually be
so your unlikely to get sanshoku while keeping tanyao My bad
( the question I gave initially will probably be
favoured more so than the edited one)
)
tsumo 
)
(dora 
)
YES