Apply suggestions from code review

Author: hfxsd

system-variables.md

@@ -5944,14 +5944,14 @@ For details, see [Identify Slow Queries](/identify-slow-queries.md).
 > - `PARALLEL` and `PARALLEL-FAST` modes are designed to reduce the average time for retrieving TS in TiDB. In situations with significant latency fluctuations, such as long-tail latency or latency spikes, these two modes might not provide any remarkable performance improvements.
 
 
-### tidb_cb_pd_metadata_error_rate_threshold_pct
+### tidb_cb_pd_metadata_error_rate_threshold_pct <span class="version-mark">New in v9.0.0</span>
 
 - Scope: GLOBAL
 - Persists to cluster: Yes
 - Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
 - Default value: `0`
 - Range: `[0, 100]`
-- This variable controls whether TiDB triggers the circuit breaker according to the error rate percentage of the specific requests sending to PD.
+- This variable controls whether TiDB triggers the circuit breaker according to the error rate percentage of the specific requests sent to PD.
 
 ### tidb_ttl_delete_rate_limit <span class="version-mark">New in v6.5.0</span>