Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Parameter | Symbol | Best fit (WMAP only) | Best fit (WMAP, extra parameter) | Best fit (all data) |
| --- | --- | --- | --- | --- |
| Age of the universe ( Ga ) | t_0 | .4 ± .3 | – | .7 ± .2 |
| Hubble's constant ( km⁄ Mpc ·s ) | H_0 | ± | ± | + − |
| ic Baryon content | \Omega_b h^2 | .024 ± .001 | .023 ± .002 | .0224 ± .0009 |
| Matter content | \Omega_m h^2 | .14 ± .02 | .14 ± .02 | .135 +.008 −.009 |
| Optical depth to reionization | \tau | .166 +.076 −.071 | .20 ± .07 | .17 ± .06 |
| Amplitude | A | .9 ± .1 | .92 ± .12 | .83 +.09 −.08 |
| Scalar spectral index | n_s | .99 ± .04 | .93 +.07 −.07 | .93 ± .03 |
| Running of spectral index | dn_s / dk | — | −.047 ± .04 | −.031 +.016 −.017 |
| Fluctuation amplitude at 8h −1 Mpc | \sigma_8 | .9 ± .1 | — | .84 ± .04 |
| Total density of the universe | \Omega_{tot} | – | – | .02 ± .02 |
Question:
What is the symbol when the best fit (WMAP, extra parameter) of –, and a Best fit (WMAP only) is .4 ± .3?
Answer:
t_0