Shuāngzǐzuò de xiàngzhēng shì yī duì shuāngbāotāi.
The symbol of Gemini is a pair of twins.
Tips
memory
双 means 'double/twin', 子 means 'child', and 座 means 'constellation/seat'. Double children = Twins = Gemini. Easy to picture two little kids side by side.