भारतीय मानक वर्गीकरण के अनुसार, प्रथम श्रेणी की इमारती लकड़ी (First class timber) का औसत जीवनकाल कितना होता है?

Which of the following artificial stones is produced by moulding a mixture of iron slag and Portland cement?

Enamel paint is generally prepared by adding:

Dorry's testing machine is used for which test on building stones?