问题如下：
which of the following statements about Corporate Credit Markets in the time of COVID-19 is incorrect?
选项：
A. Conditions in the corporate credit markets have deteriorated sharply since late February on the back of rising credit and liquidity risks.
B. Investment grade bond spreads narrowed, as investors started to focus on a large share of BBB credits that are at risk of downgrades and reduce leverage in this market segment.
C. Several central banks rolled out new facilities and expanded existing programs to support issuance and liquidity in corporate debt and commercial paper markets.
D. Strains in the risky credit market segments—high-yield bonds, leveraged loans, and private debt—continued to be evident through early April.
解释：
B is correct
Investment grade bond spreads widened, as investors started to focus on a large share of BBB credits that are at risk of downgrades and elevated leverage in this market segment.B选项错在两个地方，投资级债券的利差是扩大的，杠杆增加了而不是减少的。想顺带问下 基础班讲义157页 commercial paper spreads widened dramatically 以及159页的corporate spreads had continued to tighten 都是想表达难融资 信用变差的意思吧？ 那为什么描述上一个是spread变widened 一个是tighten?
