有關英文時態的詢問

Your sentence is correct.

Simple past tense is used to describe an action which happened at one particular time in the past, or time is stated in thr sentence.

eg. I wrote a letter yesterday.

Present perfect tense is used to describe an action happened in the past, exact time is not important, or not stated in the sentence.

eg. I have written a letter.

冇用錯呀。

Simple past tense 已經足夠了，除非你好想同你個friend强調你買左部電腦，咁既情況就用 present perfect tense，即 I have bought a computer last Thursday.

另外，present tense 都冇錯，因為你係講緊部電腦而家係新，對比之下，如果你用 past tense (It was new.) ，咁即係暗示部野舊時係新淨，而家已經唔係了，是舊貨了。

故此，你既 tense 用得岩。