1) I often read a book - Pr. Simple
2)I am reading a book now - Pr. Cont.
3) I have read a book by 12 o'clock - Pr. Perf.
4) I have been reading a book since morning - Pr. - Perfect Cont.
5) I read a book yesterday - Past Simple
6) I was reading a book at 5 o'clock yesterday - Past Cont.
7) I had read a book by the time mum came back - Past Perf.
8) I had been reading a book for 2 hours by the time mum came back - Past Perf.- Cont.