1. The following is the bar graph showing the number of boys and girls of special activity classes in Mina's school.

2. Survey the number of students according to each grade, the number of teachers, and the number of classes of your school.
1) Decide the contents which will be investigated.
2) Draw the graphs about the contents of the survey of each group and write sentences in English as in the example.
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Are the sentences above all grammatical?
Would you check them and let me know incorrect expressions?

Everything looks good except I'm rather confused about 2).

"2) Draw the graphs<~~There's already a graph, right? Are the students supposed to draw a new graph or more than one new graph? about the contents of the survey of each group and write sentences in English as in the example."

??

To check the grammaticality of the sentences, we will review them one by one:

1. The following is the bar graph showing the number of boys and girls of special activity classes in Mina's school.
This sentence is grammatically correct. It introduces a bar graph that displays the number of boys and girls in special activity classes at Mina's school. No grammatical errors are present.

2. Survey the number of students according to each grade, the number of teachers, and the number of classes in your school.
This sentence is grammatically correct. It instructs the reader to conduct a survey on three different aspects: the number of students by grade, the number of teachers, and the number of classes in their school. No grammatical errors are present.

1) Decide the contents which will be investigated.
This sentence is grammatically correct, although it can be improved by replacing "which" with "that" because the word "contents" is referring to specific items, not selections from a set. So, the corrected sentence would be: "Decide the contents that will be investigated."

2) Draw the graphs about the contents of the survey for each group and write sentences in English as in the example.
This sentence is grammatically correct. It instructs the reader to draw graphs for each group based on the survey contents and write sentences in English following the provided example. No grammatical errors are present.

Overall, except for a minor improvement in sentence 1), all the sentences are grammatically correct.