1选择题
Look at the picture. The ruler is 15 _______ long.
答案：B
解析：本题考查长度单位的选择。图片中通常显示的是学生用尺子，长度在15厘米左右是合理的。易错点是混淆mm（毫米）、cm（厘米）、m（米）和km（千米）的适用场景。
2选择题
Tom has 12 apples. He gives 5 to his sister. How many does he have now?
答案：A
解析：本题考查20以内的减法。12-5=7。易错点是计算时忘记退位或看错数字。
3选择题
There are 4 books on the desk. The number of pencils is 3 times the books. How many pencils are there?
答案：C
解析：本题考查“倍的认识”。铅笔的数量是书的3倍，即4×3=12。易错点是将“倍”理解为“多”而用加法。
4选择题
It's 3:00 p.m. in 24-hour clock. What time is it?
- A. 3:00 a.m.
- B. 13:00
- C. 15:00
- D. 23:00
答案：C
解析：本题考查24时计时法。下午3时转换为24时计时法是15时。易错点是直接将下午时间加12小时，但忘记写“时”或格式错误。
5填空题
245 + 378 = _______
答案：623
解析：本题考查万以内的加法（进位）。计算时需注意个位5+8=13，向十位进1；十位4+7+1=12，向百位进1；百位2+3+1=6。易错点是忘记进位或进位计算错误。
6填空题
A rectangle has a length of 8 cm and a width of 5 cm. Its perimeter is _______ cm.
答案：26
解析：本题考查长方形周长计算。周长 = (长 + 宽) × 2 = (8 + 5) × 2 = 26 cm。易错点是忘记乘以2，或者将长和宽相加后未再乘2。
7填空题
There are 36 students in a class. 1/4 of them are girls. The number of girls is _______.
答案：9
解析：本题考查分数的初步认识。求36的1/4是多少，即36 ÷ 4 = 9。易错点是混淆“几分之一”与“几分之几”，或计算错误。
8解答题
A school bus can carry 45 students. There are 6 such buses. How many students can they carry in total? Please show your calculation.
答案：45 × 6 = 270 (students)
They can carry 270 students in total.
解析：本题考查多位数乘一位数（进位）。计算45×6：先算5×6=30，写0进3；再算4×6=24，加上进位的3得27，结果为270。易错点是忘记进位或计算顺序错误。