B2. Karel has a large quantity of apples and pears. He wants to choose ten pieces of fruit from these and arrange them in a row. This must be done in such a way that there is never a pear between two apples. The rows AAAAAAAAAA and AAPPPPPPPP are allowed, for example, but the rows AAPPPPPPPA and APPPPPPPAA are not.

How many rows can Karel make like this?
B2. 56 There is one row with only pears. Now we count the rows with at least one apple. In such a row, all apples must be directly next to each other, because there can never be a pear between two apples. For example, if we want to choose 8 apples, they can be in positions $1 \mathrm{t} / \mathrm{m} 8$, in positions $2 \mathrm{t} / \mathrm{m} 9$, or in positions $3 \mathrm{t} / \mathrm{m} 10$, a total of three possibilities. In this way, we find 1 row for 10 apples, 2 rows for 9 apples, 3 rows for 8 apples, and so on, up to 10 rows for 1 apple. In total, we find $1+2+3+\cdots+10=55$ rows with at least one apple. The total number of rows is therefore $55+1=56$.