investment of surplus borrowings

Kaplan study text says: With regards to borrowing costs relating to specific borrowings used for the construction of a qualifying asset, match the description to the correct accounting treatment in the table below. 1. Interest earned on the investment of surplus borrowings "during the construction period" is -> Included in calculation of NCA. 2. Interest incurred "during the construction period." is -> Included in calculation of NCA. I'm having questions. - Is the first type of interest directly attributable to the construction? How come? (I based on IAS 23, para 8) - IAS 23, para 12 states: "To the extent that an entity borrows funds specifically for the purpose of obtaining a qualifying asset, the entity shall determine the amount of borrowing costs eligible for capitalisation as the actual borrowing costs incurred on that borrowing during the period less any investment income on the temporary investment of those borrowing." Does this paragraph imply that the above investment income which may started before the construction is incurred during the period also? If it is the case then the first type of interest should be investment income instead of capitalised, isn't it?