interest vs. interestingly

[Manoo]

English Language Tests, Intermediate level

ESL/EFL Test #149 "Financial and bank expressions", question 2

I decided to invest in the commodities market, as the ......... on offer from the bank was at an all-time low.

(a) increase
(b) interest
(c) rent
(d) tax

English Language Tests, Intermediate level

ESL/EFL Test #149 "Financial and bank expressions", answer 2

I decided to invest in the commodities market, as the interest on offer from the bank was at an all-time low.

Correct answer: (b) interest
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what is the answer to this question?

[Gray]

Interestingly, it is interest!
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First lesson - English, not english. I, not i. ~A student of English