(d) Different combination groups containing purine and pyrimidine
| Group X1 | Group X2 | Group X3 | |
|---|---|---|---|
| Group X4 | 41: dUTP | 37: dATP | 39: dTTP |
| Group X5 | 42: xanthine | 43: hypoxanthine | 40: dCTP |
| 38: dGTP | 38: dGTP | 38: dGTP |
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