Adverse Effect coding

Hi everybody, I'm taking ICD-10 online class from AAPC. But I'm confused, because the work book and online lecture are not matching. Here is the question.

A patient took a dose of penicillin that was prescribed correctly resulting in projectile vomiting.

A) R11.12 Projectile vomiting

T36.0X5A Adverse effect of penicillin, initial encounter

B) T36.0X5A Adverse effect of penicillin, initial encounter

R11.12 Projectile vomiting

Which answer is correct?? A or B? Work book says A, but online lecture says B..

If the sequence is same as ICD-9, then A is correct I believe, but how about ICD-10?

Please help!

Thanks.

Adverse Effect coding