Group relief groups.

Hello sir, below is a qn from the kaplan exam kit

Telephone Ltd prepares accounts to 31 March each year. Throughout the year ended
31 March 2022 Telephone Ltd owned 62% of Desk Ltd, 75% of Chair Ltd, 55% of Table Ltd (a
dormant company) and 100% of Window Inc (resident overseas). Telephone Ltd acquired
60% of the share capital of Curtain Ltd on 1 January 2021.
What is the total number of companies for the purposes of adjusting the £1,500,000
augmented profits threshold of Telephone Ltd for the year ended 31 March 2022?
A 2
B 3
C 4
D 5

the answer is C) 4. However i don’t understand why its not D)5, why do we not include curtain ltd.
After all it was bought during the previous accounting period, therefore is it deemed to be part of the group from the beginning of this accounting period which starts at 1st April 2021.