wǒ / bú shì / bù xiǎng / huí dá / zhǐ shì / lín chǎng / yì / jǐn zhāng / jiù / zuǐ dùn

我不是不想回答，只是临场一紧张就嘴钝。

It is not that I do not want to answer; I just become inarticulate when I get nervous on the spot.