一正弦交流电的电压随时间变化规律如图，则该交流电

鸦片战争后，英国提出“协定关税”；甲午中日战争后，日本又取得“在华设厂”的特权。这两者的共同点是 (　　)

科学家研究某区域中田鼠的种群数量变化，得到该种群在数年内的出生率和死亡率的比值曲线如图（其中R= $\frac{出生率}{死亡率}$ ）．在不考虑迁入迁出的情况下，下列说法正确的是（　　）

二战后，西欧、日本经济迅速恢复和发展的共同原因是（    ）

①建立了区域合作    ②采用先进的科学技术成果  ③制定了适当的经济政策    ④美国的经济援助

阅读下面短文，在空白处填入一个适当的词，或填入括号中所给单词的正确形式。    I had my summer all planned out．I was going to enjoy the city． However, my parents had ____ different idea．They said l would be going to my grandparents' farm ____ a whole month．I felt sad．What could ____ (possible)be fun to do in the country?
    It was very hot when we arrived at the farm．So Grandpa took ____ (I)to a creek(小溪)．It felt great to jump into the cool，clear water．I ____ (begin)to think staying in the country might be ____ (interesting)than I had thought．
    The next day Grandma gave me a basket and sent me out ____(pick)strawberries．The berries were so good that a lot of them had disappeared ____ they reached my basket．
    I didn't get to visit a zoo， but l got an up-close look at pigs，cows，and ____ (chicken)．I fed the goats，milked the cows，and collected fresh eggs．
    My summer wasn't what I had expected，____ I loved it! I was sad that I had to leave．Now, I still love living in the city，but I learned that trying new things can be a lot of fun，too!