He began to learn English _____ (in / at) the age of six
句意：他六岁开始学英语。at the age of…在几岁，固定搭配，故选 at。
2018年12月，张阿姨把4000元的存入银行，定期三年，年利率是2.75%到期后，应得利息______元.
Her mother will come back _____ (after / in) five days.
Autumn comes _____ (before / after) summer.
What do you often do _____ (at / in) weekends?