"kemudian" and "lalu" is completely interchangeable. this one doesn't allow the former.
Are "terus", "setelah", and "selepas" also acceptable here?
The English sentance is past tense, so I wrote "Kereta ini telah dipercepat lalu diperlambat" but it was not accepted. Is my translation wrong?
"Telah" is used for past perfect. Simple past tense doesn't exist in Indonesian, it depends solely on context.
Thanks, that was a nuance I hadn't identified.