TS Police SI Mains 2018 Paper 4

Which of the following statements is/are correct ?
a. India's foreign exchange reserves declined from $7\mathit{b}\mathit{i}\mathit{l}\mathit{l}\mathit{i}\mathit{o}\mathit{n}\mathit{d}\mathit{o}\mathit{l}\mathit{l}\mathit{a}\mathit{r}\mathit{s}\mathit{i}\mathit{n}1979-80\mathit{t}\mathit{o}\mathit{j}\mathit{u}\mathit{s}\mathit{t}$600 million dollars in January 1991.
b. In 1979-80, India's foreign debt was $18\mathit{b}\mathit{i}\mathit{l}\mathit{l}\mathit{i}\mathit{o}\mathit{n}\mathit{d}\mathit{o}\mathit{l}\mathit{l}\mathit{a}\mathit{r}\mathit{s}\mathit{a}\mathit{n}\mathit{d}\mathit{b}\mathit{y}\mathit{M}\mathit{a}\mathit{r}\mathit{c}\mathit{h},1991\mathit{i}\mathit{t}\mathit{h}\mathit{a}\mathit{d}\mathit{r}\mathit{i}\mathit{s}\mathit{e}\mathit{n}\mathit{t}\mathit{o}$90 billion dollars.
The correct answer is :