address comments

choose-index.md

@@ -29,7 +29,7 @@ Before introducing index selection, it is important to understand the ways TiDB
 
 ## Index selection rules
 
-TiDB selects indexes based on rules or cost. the based rules include pre rules and Skyline-pruning. When selecting an index, TiDB tries the pre rule first. If an index satisfies a pre rule, TiDB directly selects the index. Otherwise, TiDB uses Skyline-pruning to exclude unqualified indexes, and then based on the cost estimation of each operator for accessing tables, selects the index with the lowest cost.
+TiDB selects indexes based on rules or cost. The based rules include pre rules and skyline-pruning. When selecting an index, TiDB tries the pre rule first. If an index satisfies a pre rule, TiDB directly selects the index. Otherwise, TiDB uses skyline-pruning to exclude unsuitable indexes, and then based on the cost estimation of each operator for accessing tables, selects the index with the lowest cost.
 
 ### Selection based on rules
 
@@ -78,9 +78,9 @@ Skyline-pruning is a heuristic filtering rule for indexes, which can reduce the
 
 - How many access conditions are covered by the indexed columns. An "access condition" is a where condition that can be converted to a column range. And the more access conditions an indexed column set covers, the better it is in this dimension.
 
-For these three dimensions, if the index `idx_a` is not worse than the index `idx_b` in all three dimensions and one of the dimensions is better than `idx_b`, then `idx_a` is preferred. When executing the `EXPLAIN FORMAT = 'verbose' ...` statement, if Skyline-pruning excludes some indexes, TiDB will output a NOTE level warning listing the reserved indexes after Skyline-pruning's exclusion.
+For these three dimensions, if the index `idx_a` is not worse than the index `idx_b` in all three dimensions and one of the dimensions is better than `idx_b`, then `idx_a` is preferred. When executing the `EXPLAIN FORMAT = 'verbose' ...` statement, if skyline-pruning excludes some indexes, TiDB will output a NOTE level warning listing the reserved indexes after skyline-pruning's exclusion.
 
-In the following example, the index `idx_b` and `idx_e` are both inferior to `idx_b_c`, so they are excluded by Skyline-pruning. The returned result of `SHOW WARNING` displays the remaining indexes after Skyline-pruning.
+In the following example, the index `idx_b` and `idx_e` are both inferior to `idx_b_c`, so they are excluded by skyline-pruning. The returned result of `SHOW WARNING` displays the remaining indexes after skyline-pruning.
 
 ```sql
 mysql> CREATE TABLE t(a INT PRIMARY KEY, b INT, c INT, d INT, e INT, INDEX idx_b(b), INDEX idx_b_c(b, c), INDEX idx_e(e));
@@ -105,7 +105,7 @@ mysql> SHOW WARNINGS;
 
 ### Selection based on cost estimation
 
-After using the Skyline-pruning rule to rule out inappropriate indexes, the selection of indexes is based entirely on the cost estimation. The cost estimation of accessing tables requires the following considerations:
+After using the skyline-pruning rule to rule out inappropriate indexes, the selection of indexes is based entirely on the cost estimation. The cost estimation of accessing tables requires the following considerations:
 
 - The average length of each row of the indexed data in the storage engine.
 - The number of rows in the query range generated by the index.