Why my Read Aloud voice is changing between two lines in Office 365?

I have a Word document with only two lines as below.

Word Number 2 is. Acquaintance. spelt as
Word Number 2 is. Acquaintance. spelt as a c q u a i n t a n c e

When I click speak Aloud, it speaks line 1 in a British tone and line 2 in some European tone. 

Please can someone guide how to stick to a British tone only?

I have noticed that the voice tone is also changed when it encounters the below words in the line, not sure what is so special in these words that causes it to change its tone.

a c q u a i n t a n c e

i n c o n v e n i e n c e

e m b a r r a s s m e n t

m i s u n d e r s t a n d i n g

d i s a g r e e m e n t

r e c o m m e n d a t i o n

c o m p r e h e n s i o n

t r a n s m i s s i o n

m a t h e m a t i c i a n

s t a t i s t i c i a n