निम्नलिखित में से कौन-सा प्राकृतिक पत्थर सबसे अधिक अग्नि-प्रतिरोधी विशेषताएँ प्रदर्शित करता 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?