[单选题]
Two stars of equal mass7ucd,p-d bo 6/amiua5 gp,42wfsbm g: )zf;ww $M$ are shown in the diagram, distance $d$ apart. A planet is equidistant from the two stars, with distance $\frac{d}{s}$ across the midpoint of the line joining the stars as shown.
What is the resultant gravitational field strength at the position of the planet due to the two star
A. $2\frac{GM}{d^2}\cos 45^{\circ}C$
B. $4\frac{GM}{d^2}\cos 45^{\circ}C$
C. $2\frac{GM}{d^2}\tan 45^{\circ}C$
D. $4\frac{GM}{d^2}\tan 45^{\circ}C$
