Concept:English word order for adverbs: manner comes before place and time.
Explanation:The main verb in the sentence is "practising".
The word "hard" is an adverb of manner that describes how the footballers are practising.
An adverb of manner must be placed immediately after the verb it modifies.
Therefore, "hard" must come directly after "practising".
Next, the adverb of place "in the stadium" tells us where the practising took place.
Finally, the adverb of time "all morning" tells us when the practising took place.
The correct sequence is: verb + manner + place + time.
Only option A follows this natural order.
Options B, C, and D scramble this order and sound awkward and ungrammatical.
Answer:A. hard in the stadium all morning