Answer:
d. john found writing boring
Explanation:
From the four (4) given reasons/options, the reason why he's not good at writing is option (d).
The reason is as follows:
(a) Not having English as a first language does not necessarily mean one can not be good at writing
(b) There is no information regarding his parent's efforts in his writing skill. So, there is no enough information to go with option (b).
(c) The fact that he is a writer negates this option
(d) Of all the given options, this is the most suitable reason that may hinder his writing skills. Although he is a writer, it is also possible that he gets bored when writing.
Definitely, this will reduce his interest in writing and hinder his writing skills.