choose

[adill]

Hamdi is very fast. I think he...................in the
Olympic Games one day!
a- would be b- is going to be c- is d- will be

[مستر ابو عبد الرحمن]

will be
لان very fast صفة شخصية
و الصفات الشخصية لا تعد دليل

[Mohammed Etify]

Only when you see present evidence, can you choose " gong to" for prediction. being fast is no evidence. Running faster distance than other contestants is what we call call evidence.
So, here it is " will"