Which of the following pairs are correctly matched ?

1. Primary sex ratio — Sex at the time of conception
2. Secondary sex ratio — Sex at the time of birth
3. Tertiary sex ratio — Sex at the time of enumeration
4. Imbalanced sex ratio—Sex of workers

Select the correct answer using the codes given below:
(a) 1, 2, 3 and 4
(b) 1, 3 and 4
(c) 2 and 4
(d) 1, 2 and 3