pls check this multiple choice question

[meridiem]

I couldn't understand why the correct answer is as follows:

As a teenager, my brother always ....... the same tune when he ....... a shower.

I give you two options which I think confusing;
a) whistles/ takes
b) whistled/ was taking

The correct answer is said to be (b). Could someone please tell me the reason or whether that one is the corret one?

[Temico]

"As a teenager" refers to a time in the past, so the use of verbs in the past tense is correct. Other examples:-

1. As a boy, my father used to go fishing a lot.
2. As a girl, my mother worked as an air hostess.