Q$\mathrm{.}9)$ A bid for foundation construction is based on ownex supplied soil boring test results showing sandy clay to a depth of $6m.$ However during construetion the brekhoe encounters Large pieces of conerete burted throughout the construction site. This$-$situation would normally be referred to a s$?$

a$)$ A concealed conditions

b$)$ Unexplained features

b$)$ Unexpected characteristics

in Hitden detriment