Sentence Correction

In the following question (Q no. 145 of OG):

Most state constitutions now mandate that the state budget be balanced each year.
(A) mandate that the state budget be balanced
(B) mandate the state budget to be balanced
(C) mandate that the state budget will be balanced
(D) have a mandate for a balanced state budget
(E) have a mandate to balance the state budget

OG's answer (Choice A) says that "When mandate is used as a verb to mean "make it mandatory,' it must be followed by that and a verb in the
subjunctive mood"
But this this is the first time i am reading this time of rule when there r thousands of places (which can be trusted for their grammar) use verb 'mandate' without 'that'. A simple and trustable example is Cambridge dictionary:

https://dictionary.cambridge.org/define. ... &dict=CALD

which demonstrate such use of mandate in its example sentence.

Is it something else which makes Choice A to be correct or the answer itself is wrong ..
i m really not sure whether i can trust OG answers fully or not. I found this kinda wrong things in many other questions too.

And shall i blindly accept and follow what OG says .. bcoz it is 'Official' ?

The GMAT definitely tests the subjunctive and the accredited answer to this question would also be the accredited answer on test day.

If you ask 10 grammarians about English, you'll likely get 15 different opinions about what's correct. The key to success on the GMAT is learning what GMAC considers correct and then adopting those rules.

While the OG has many flaws, it does include an accurate representation of the real SC questions you'll see on the GMAT,

i can blindly follow it then ...
Thank u Stuart ...