英语语法分析

At present, surveying gravitational field and its variation with time accurately and detailedly is a main subject of Gravisat.

精密和详细测定地球重力场及其时间变化，是目前卫星重力测量的主要课题。

It is a main subject of Gravisat at present that we survey gravitational field and variety of gravitational field with time accurately in detail.

精密和详细测定地球重力场及其随时间变化，是目前卫星重力测量的主要课题。