The least number of 4-digits which is exactly divisible by 9 is
(a) 1008 (b) 1009 (c) 1026 (d) 1018

Least 4-digit number = 1000

$$\begin{gathered} 111 \\ 9\overline{)1000} \\ \underline{-9} \\ 10 \\ \underline{-9} \\ 10 \\ \underline{-9} \\ 1 \end{gathered}$$

The least 4-digit number exactly divisible by 9 is 1000 + (9 − 1) = 1008.
Hence, the correct option is (a).